openstack: Implement backend and test suite

[cej-harris]

Implements a backend enabling the use of an OpenStack environment to be used by runner-manager.

• Configured using either environment variables or clouds.yaml (as implemented by openstacksdk)
• The test suite can be run either against a real OpenStack environment (by setting the USE_LIVE_OPENSTACK environment variable to "true" and configuring the parameters required by openstacksdk)
  • If a real OpenStack environment is not available a number of mock classes are implemented to simulate an OpenStack environment
  • test_mock_signatures ensures that the mock interfaces matches the interfaces provided by openstacksdk

I've tested this against an OpenStack environment available to me and the runners spawned function and register correctly in Github.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.51948% with 15 lines in your changes missing coverage. Please review.

Project coverage is 86.68%. Comparing base (bdf1fcf) to head (e036670).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
runner_manager/backend/openstack.py	75.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #685      +/-   ##
==========================================
- Coverage   86.74%   86.68%   -0.06%     
==========================================
  Files          34       35       +1     
  Lines        1433     1510      +77     
==========================================
+ Hits         1243     1309      +66     
- Misses        190      201      +11     

Flag	Coverage Δ
api	63.90% <45.45%> (-1.00%)	⬇️
unit	68.41% <80.51%> (+0.92%)	⬆️

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[cej-harris]

I think the Docker build fails because netifaces requires the python3-dev package to be installed. In testing I think I got around this by changing the base image from python3.11-slim to python3.11 and forgot to include it as part of this PR. Alternatively it should be possible to install the python3-dev package on top of the slim image, but this negates some of the benefits from using the slim image.

If there's still a need for a small image size, I believe it should be possible to use a multi-stage build to install netifaces in the full Python base image and copy the Python environment and other required files into the slim Python base image.

Let me know which option you prefer and I'll have a go at implementing and testing it.

[tcarmet]

First of all, thank you so much for this pr @cej-harris, we were also planning to develop an openstack backend at some point, so this is a very welcome contribution!

And in regards to the Dockerfile let's stop using the slim go for python:3.11 seems like healthiest approach to solve the issue.