feat(rally-tests): Adds OpenStack Rally scenario for testing Octavia Load Balancers

[nicholaskuechler]

Adds a rally scenario for building octavia load balancers.

Example output:

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Task 235e1680-d002-469a-ba66-48ff9c5fe6c8 has 0 error(s)
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+----------------------------------------------------------------------------------------------------------------------------------------+
|                                                          Response Times (sec)                                                          |
+-------------------------------------+-----------+--------------+--------------+--------------+-----------+-----------+---------+-------+
| Action                              | Min (sec) | Median (sec) | 90%ile (sec) | 95%ile (sec) | Max (sec) | Avg (sec) | Success | Count |
+-------------------------------------+-----------+--------------+--------------+--------------+-----------+-----------+---------+-------+
| octavia.load_balancer_create        | 10.605    | 10.605       | 10.605       | 10.605       | 10.605    | 10.605    | 100.0%  | 1     |
| octavia.wait_for_loadbalancers      | 2.774     | 2.774        | 2.774        | 2.774        | 2.774     | 2.774     | 100.0%  | 1     |
|  -> octavia.load_balancer_show (x2) | 0.773     | 0.773        | 0.773        | 0.773        | 0.773     | 0.773     | 100.0%  | 1     |
| octavia.load_balancer_delete        | 0.35      | 0.35         | 0.35         | 0.35         | 0.35      | 0.35      | 100.0%  | 1     |
| total                               | 13.729    | 13.729       | 13.729       | 13.729       | 13.729    | 13.729    | 100.0%  | 1     |
|  -> duration                        | 13.729    | 13.729       | 13.729       | 13.729       | 13.729    | 13.729    | 100.0%  | 1     |
|  -> idle_duration                   | 0.0       | 0.0          | 0.0          | 0.0          | 0.0       | 0.0       | 100.0%  | 1     |
+-------------------------------------+-----------+--------------+--------------+--------------+-----------+-----------+---------+-------+

Load duration: 13.728859
Full duration: 103.695137