Fix loadgenerator race condition

[TheRealSpaceShip]

Handle to avoid calls of authenticated endpoints when logout has already been called

Background

Almost 50% of authenticated requests are failing with error code 401 because of the request-logout race.

Change Summary

Fixed logic on how signup+login and logout works. Also made some small improvements.

[bourgeoisor]

Lint is failing:

Run> pylint --rcfile=./.pylintrc ./src/*/*.py
************* Module locustfile
src/loadgenerator/locustfile.py:[5](https://github.com/GoogleCloudPlatform/bank-of-anthos/actions/runs/3264911106/jobs/5368966183#step:5:6)3:12: R1705: Unnecessary "else" after "return" (no-else-return)

[bourgeoisor]

The load generator seems to be more in-line with failure expectations:

Type     Name                                                                          # reqs      # fails |    Avg     Min     Max    Med |   req/s  failures/s
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
GET      /                                                                               6385     0(0.00%) |     97      24    9454     35 |    1.20        0.00
POST     /deposit                                                                        3830     9(0.23%) |    382     139   13230    310 |    0.30        0.00
GET      /home                                                                           6194     0(0.00%) |     89      23    6076     33 |    1.00        0.00
GET      /login                                                                          3576    11(0.31%) |     19       2    7240      5 |    0.00        0.00
POST     /login                                                                          3124     0(0.00%) |   3227    1313   10527   3100 |    0.40        0.00
POST     /logout                                                                          635     0(0.00%) |     37       6    3824      9 |    0.00        0.00
POST     /payment                                                                        3105    16(0.52%) |    379      69    5129    310 |    0.60        0.00
GET      /signup                                                                         3483     4(0.11%) |     28       2   15380      5 |    0.00        0.00
POST     /signup                                                                          665    25(3.76%) |   4603       2   14009   4300 |    0.00        0.00
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
         Aggregated                                                                     30997    65(0.21%) |    553       2   15380     51 |    3.50        0.00

Vs. what's currently in the main branch:

Type     Name                                                                          # reqs      # fails |    Avg     Min     Max    Med |   req/s  failures/s
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
GET      /                                                                               7783     0(0.00%) |     48       2    8687     28 |    0.90        0.00
POST     /deposit                                                                        4623 2267(49.04%) |    193       2    8401    290 |    0.70        0.10
GET      /home                                                                           7912 3874(48.96%) |     49       4    8553     27 |    0.90        0.30
GET      /login                                                                          2008     0(0.00%) |     14       2    3254      4 |    0.20        0.00
POST     /login                                                                          3867 1859(48.07%) |   1415       2    9517   1400 |    0.40        0.00
POST     /logout                                                                          743     0(0.00%) |     22       5    1066      9 |    0.30        0.00
POST     /payment                                                                        3822 1877(49.11%) |    189       2    7293    290 |    0.20        0.00
GET      /signup                                                                         2058     0(0.00%) |     16       2    3143      5 |    0.20        0.00
POST     /signup                                                                          386    11(2.85%) |   3987    1858   11911   3600 |    0.10        0.00
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
         Aggregated                                                                     33202 9888(29.78%) |    285       2   11911     10 |    3.90        0.40

[bourgeoisor]

After latest commit:

Type     Name                                                                          # reqs      # fails |    Avg     Min     Max    Med |   req/s  failures/s
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
GET      /                                                                                433     0(0.00%) |    173      32    8063     57 |    0.40        0.00
POST     /deposit                                                                         272     0(0.00%) |    558     300    8330    350 |    0.40        0.00
GET      /home                                                                            438     0(0.00%) |    208      30    8041     58 |    0.60        0.00
GET      /login                                                                           265     0(0.00%) |     63       3    2759      5 |    0.00        0.00
POST     /login                                                                           200     0(0.00%) |   4881    1576   12607   4500 |    0.40        0.00
POST     /logout                                                                           40     0(0.00%) |     99       8    2469     10 |    0.00        0.00
POST     /payment                                                                         228     9(3.95%) |    695     304   11205    350 |    0.30        0.00
GET      /signup                                                                          245     0(0.00%) |     15       3    1062      5 |    0.00        0.00
POST     /signup                                                                           61   16(26.23%) |   5893      38   13932   4900 |    0.10        0.00
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
         Aggregated                                                                      2182    25(1.15%) |    842       3   13932     77 |    2.20        0.00

Looks great!

[bourgeoisor]

LGTM