Delete LXD instance if LXD failed to remove ephemeral instance

[yhaliaw]

Fix a resource leak problem when LXD failed to remove an ephemeral instance on stop.

This PR includes:

• Delete LXD ephemeral instance that LXD failed to remove.
• Installs pylxd from source on GitHub to fix a bug in version on PyPI. See this comment.

[github-actions]

Test coverage for e25f299

Name                    Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------------
src/charm.py              252     39     50      9    83%   238, 254-256, 265-266, 273, 284, 295->312, 300-305, 322-323, 327-328, 333-336, 352-353, 387-395, 425-427, 430->exit, 434-436, 459-464, 496
src/errors.py              18      0      0      0   100%
src/event_timer.py         42      8      4      0    74%   96-99, 119-122
src/github_type.py         36      0      0      0   100%
src/lxd_type.py            24      0      0      0   100%
src/runner.py             184     31     46     14    80%   135-155, 223, 260-262, 269, 283, 293, 312, 346-351, 361, 408, 441, 467, 472-484, 498, 516
src/runner_manager.py     189     20     80      8    88%   189-190, 204-210, 214-216, 226-227, 278, 302-306, 325, 343, 456, 476
src/runner_type.py         43      0     10      0   100%
src/utilities.py           55      2     12      4    91%   74->76, 78->84, 89-91
-------------------------------------------------------------------
TOTAL                     843    100    202     35    86%

Static code analysis report

Run started:2023-05-12 03:04:12.387503

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1822
  Total lines skipped (#nosec): 0
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 9

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):

[sirkadirov]

@yhaliaw Glad that my comment helped you 😊! And yeah, sometimes LXD fails to delete ephemeral instances... I admit, I didn't think that an additional call to the container removal function could improve the situation. Thanks for the idea, I'll try it out in my project.