DAOS-623 ci: avoid exception in extra.py when clang-format is missing

[grom72]

To avoid extra.py script corruption when clang-format is not installed.

Traceback (most recent call last):
  File "/home/grom72/repos/daos/./site_scons/site_tools/extra/extra.py", line 141, in <module>
    main()
  File "/home/grom72/repos/daos/./site_scons/site_tools/extra/extra.py", line 105, in main
    supported = _supports_correct_style(WhereIs('clang-format'))
  File "/home/grom72/repos/daos/./site_scons/site_tools/extra/extra.py", line 51, in _supports_correct_style
    rawbytes = subprocess.check_output([clang_exe, "-version"])
  File "/usr/lib64/python3.9/subprocess.py", line 424, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/usr/lib64/python3.9/subprocess.py", line 505, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/lib64/python3.9/subprocess.py", line 951, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib64/python3.9/subprocess.py", line 1712, in _execute_child
    and os.path.dirname(executable)
  File "/usr/lib64/python3.9/posixpath.py", line 152, in dirname
    p = os.fspath(p)
TypeError: expected str, bytes or os.PathLike object, not NoneType

Doc-only: true

Before requesting gatekeeper:

• Two review approvals and any prior change requests have been resolved.
• Testing is complete and all tests passed or there is a reason documented in the PR why it should be force landed and forced-landing tag is set.
• Features: (or Test-tag*) commit pragma was used or there is a reason documented that there are no appropriate tags for this PR.
• Commit messages follows the guidelines outlined here.
• Any tests skipped by the ticket being addressed have been run and passed in the PR.

Gatekeeper:

• You are the appropriate gatekeeper to be landing the patch.
• The PR has 2 reviews by people familiar with the code, including appropriate owners.
• Githooks were used. If not, request that user install them and check copyright dates.
• Checkpatch issues are resolved. Pay particular attention to ones that will show up on future PRs.
• All builds have passed. Check non-required builds for any new compiler warnings.
• Sufficient testing is done. Check feature pragmas and test tags and that tests skipped for the ticket are run and now pass with the changes.
• If applicable, the PR has addressed any potential version compatibility issues.
• Check the target branch. If it is master branch, should the PR go to a feature branch? If it is a release branch, does it have merge approval in the JIRA ticket.
• Extra checks if forced landing is requested
  • Review comments are sufficiently resolved, particularly by prior reviewers that requested changes.
  • No new NLT or valgrind warnings. Check the classic view.
  • Quick-build or Quick-functional is not used.
• Fix the commit message upon landing. Check the standard here. Edit it to create a single commit. If necessary, ask submitter for a new summary.

[github-actions]

Ticket title is 'Generic ticket for minor code cleanup and improvement'
Status is 'Resolved'
Labels: 'request_for_2.6.3'
https://daosio.atlassian.net/browse/DAOS-623

[daosbuild1]

Test stage Python Bandit check completed with status FAILURE. https://build.hpdd.intel.com//job/daos-stack/job/daos/view/change-requests/job/PR-15762/2/execution/node/133/log

[grom72]

@daltonbohning please take a look at one more changes set to improve scripts usability