CP-48198: Fix running pytest on tests/integration in GitHub CI (with coverage)

[bernhardkaindl]

This PR includes a number of fixes / improvements for the tests:

Improve tests so that tests/integration/*.py can contribute to covering xen-bugtool

• .github/workflows/main.yml:
  • Fix running tests/integration in GitHub CI which use /opt/hostedtoolcache to provide Python.
  • Therefore, tests/integration needs to use /opt/xensource as mount point for the dom0 template files in /opt/xensource.
• tests/integration/utils.py: Use runpy.run_path(bugtool_script, run_name="__main__") to get coverage if the script
• tests/integration/conftest.py: Add mocks to sys.path so the mocks are found during runpy.run_path()
• .coveragerc: Update to no longer limit coverage to tests/unit but also include tests/integration.

Support running tests independent of the starting directory

• Fix places where os.getcwd() was used to get relative paths to be based on __file__.
• Pass path names to functions wherever this is feasible

Other changes

• tests/unit/test_main.py: Fix test to pass with Python 3.11

[codecov]

Codecov Report

Merging #105 (ce8002f) into master (d0e569d) will increase coverage by 3%.
Report is 19 commits behind head on master.
The diff coverage is 100%.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #105    +/-   ##
======================================
+ Coverage      88%    91%    +3%     
======================================
  Files          18     19     +1     
  Lines        2196   2242    +46     
======================================
+ Hits         1939   2058   +119     
+ Misses        257    184    -73     

Files	Coverage Δ
tests/conftest.py	100% <100%> (ø)
tests/integration/conftest.py	100% <100%> (ø)
tests/integration/test_system_load.py	100% <100%> (ø)
tests/integration/test_xenserver_config.py	100% <100%> (ø)
tests/integration/utils.py	87% <100%> (+2%)	⬆️
tests/unit/conftest.py	100% <ø> (ø)
tests/unit/test_main.py	100% <100%> (ø)
tests/unit/test_output.py	100% <100%> (ø)

... and 2 files with indirect coverage changes

Flag	Coverage Δ
python2.7	96% <100%> (+10%)	⬆️
python3.10.13	?
python3.10.14	91% <100%> (?)

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[coveralls]

Pull Request Test Coverage Report for Build 8477989884

Details

• 44 of 44 (100.0%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.8%) to 92.254%

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Totals
Change from base Build 8474976295:	1.8%
Covered Lines:	2132
Relevant Lines:	2311

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💛 - Coveralls