Enhance mechanism to cleanup old Salt Bundle environment (bsc#1228690)

[meaksh]

What does this PR change?

This PR passes SALT_HIGHSTATE=1 when calling post_start_cleanup.sh as part of the highstate. This way, we allow post_start_cleanup.sh script to detect when it is triggered by venv-salt-minion-postinstall.service or highstate.

This way, together with the changes in the post_start_cleanup.sh script done here: https://build.opensuse.org/request/show/1206496, we prevent an early cleanup of the environment by the timer when there is still running Salt Bundle upgrade action.

This helps to prevent the following exception when triggering a patch upgrade containing Salt Bundle plus lot of other patches:

The minion function caused an exception: Traceback (most recent call last):
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/minion.py", line 1917, in _thread_return
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/minion.py", line 1876, in _execute_job_function
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 149, in __call__
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 1234, in run
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 1249, in _run_as
File "/usr/lib/venv-salt-minion/lib/python3.10/site-packages/salt/executors/venv.py", line 24, in execute
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 149, in __call__
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 1234, in run
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 1249, in _run_as
File "/usr/lib/venv-salt-minion/lib/python3.10/site-packages/salt/executors/direct_call.py", line 10, in execute
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 149, in __call__
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 1234, in run
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/loader/lazy.py", line 1249, in _run_as
File "/usr/lib/venv-salt-minion/lib/python3.10/site-packages/salt/modules/state.py", line 833, in apply_
File "/usr/lib/venv-salt-minion/lib/python3.10/site-packages/salt/modules/state.py", line 1479, in sls
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/state.py", line 3555, in call_high
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/state.py", line 2723, in call_chunks
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/state.py", line 3245, in call_chunk
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/utils/decorators/state.py", line 45, in _func
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/state.py", line 2463, in call
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/state.py", line 1368, in check_refresh
File "/usr/lib/venv-salt-minion/lib64/python3.10/site-packages/salt/state.py", line 1316, in module_refresh
File "/usr/lib/venv-salt-minion/lib64/python3.10/importlib/__init__.py", line 168, in reload
ModuleNotFoundError: spec not found for the module 'site'
(code 1)

GUI diff

No difference.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

• No tests: no acceptance tests yet Salt Bundle upgrade

• DONE

Links

Issue(s): https://github.com/SUSE/spacewalk/issues/24978

• DONE

Changelogs

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• Re-run test "backend_unittests_pgsql"
• Re-run test "java_pgsql_tests"
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[meaksh]

Closing in favor of different approach here: openSUSE/salt#685