T7042: drop use of inspect module in favor of ast for source analysis

[jestabro]

Change summary

Rewrite the configd script compatibility test using the ast module instead of the inspect module. This avoids importing config mode scripts as modules, with requisite dependencies, in the build environment.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):
  Remove unnecessary restriction on build environment.

Related Task(s)

Related PR(s)

How to test / Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

👍
No issues in PR Title / Commit Title

[github-actions]

CI integration 👍 passed!

Details

CI logs

• CLI Smoketests (no interfaces) 👍 passed
• CLI Smoketests (interfaces only) 👍 passed
• Config tests 👍 passed
• RAID1 tests 👍 passed
• TPM tests 👍 passed

[sever-sever]

Tried this PR, should it fix this?

======================================================================
FAIL: test_signatures (test_configd_inspect.TestConfigdInspect.test_signatures)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/vyos/work/tmp/vyos-1x-vpp-edition/vyos-1x/src/tests/test_configd_inspect.py", line 119, in test_signatures
    self.assertEqual(sig_lens[f], 1, f"'{s}': '{f}' incorrect signature")
AssertionError: 2 != 1 : 'vpp_interfaces_bonding.py': 'get_config' incorrect signature

Still fails

[jestabro]

It should not fix that: it is correctly catching an incompatibility in the vpp* scripts (I tested the PR on the vpp* scripts; this was evidence that the PR was correct). The incompatibilty is that when configd calls the standard functions, it will only call with a single argument to get_config.