[1LP][RFR] Remove need to pin python-novaclient with s/HTTPClient/SessionClient

[bsquizz]

It appears the only reason python-novaclient was pinned was due to the library's removal of 'HTTPClient' (and apparently SessionClient provides the same interface). We had already moved to 'SessionClient' in openstack.py, but had not done it for openstack_infra.py -- the code blocks for this section in both files is pretty much identical.

[mshriver]

Changes look good, pending testing results for version conflicts.

[bsquizz]

Testing locally using test_instance_power_control with RHOS provider in integration_tests (the fixture in there relies on create_on_provider which deploys a VM template, so this should exercise 'novaclient' decently). Looks good so far.

2018-04-16 14:24:28,296 [I] ------------ test_quadicon_terminate_cancel[rhos11] result: passed ------------- (fixtures/log.py:59)
2018-04-16 14:26:57,806 [I] ---------------- test_quadicon_terminate[rhos11] result: passed ---------------- (fixtures/log.py:59)
2018-04-16 14:29:45,238 [I] ----------------------- test_stop[rhos11] result: passed ----------------------- (fixtures/log.py:59)
2018-04-16 14:34:47,806 [I] ---------------------- test_start[rhos11] result: passed ----------------------- (fixtures/log.py:59)
2018-04-16 14:39:37,936 [I] ------------------- test_soft_reboot[rhos11] result: passed -------------------- (fixtures/log.py:59)
2018-04-16 14:48:59,893 [I] ------------- test_power_on_or_off_multiple[rhos11] result: passed ------------- (fixtures/log.py:59)
2018-04-16 14:53:52,875 [I] ------------------- test_hard_reboot[rhos11] result: passed -------------------- (fixtures/log.py:59)
2018-04-16 14:58:48,045 [I] --------------------- test_suspend[rhos11] result: passed ---------------------- (fixtures/log.py:59)
2018-04-16 15:03:00,045 [I] --------------------- test_unpause[rhos11] result: passed ---------------------- (fixtures/log.py:59)
2018-04-16 15:08:14,740 [I] ---------------------- test_resume[rhos11] result: passed ---------------------- (fixtures/log.py:59)
2018-04-16 15:10:25,319 [I] -------------------- test_terminate[rhos11] result: passed --------------------- (fixtures/log.py:59)

[mshriver]

Checkout the travis build results, its failing a novaclient import.

And as I click comment the page updates with new commits, James's review, and passing checks. thx GH.

[bsquizz]

Yep travis failed on commit #1, commit #2 fixed that :)