tests(lxd): avoid failure on multiple calls to --show-log

[blackboxsw]

Rebase as separate commits

Proposed Commit Message

*  tests(minimal): rsyslog not in minimal images expect warning
    
    Adapt test_no_problems to use verify_clean_boot instead of
    verify_clean_log.
    
    Fix verify_clean_boot to retain platform-specific ignored tracebacks
    before passing it into _verify_clean_boot.

* tests(lxd): avoid failure on multiple calls to --show-log

Cope with repeated calls to lxc console --show-log which exits 1
with the error "no such file or directory" when the log entries
have already been processed and no new log entries exist.

Preserve lxc_log on the client instance and return former log content
on lxd platforms when "no such file or directory" runtime errors are raised

Additional Context

Resolves test_keys_to_console errors seen in https://jenkins.canonical.com/server-team/view/cloud-init/job/cloud-init-integration-noble-lxd_container-minimal/lastSuccessfulBuild/#showFailuresLink

Test Steps

 CLOUD_INIT_OS_IMAGE_TYPE=minimal CLOUD_INIT_PLATFORM=lxd_container CLOUD_INIT_CLOUD_INIT_SOURCE=IN_PLACE CLOUD_INIT_OS_IMAGE_TYPE=minimal CLOUD_INIT_OS_IMAGE=jammy tox -e integration-tests -- --last-failed tests/integration_tests/modules/test_keys_to_console.py

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[a-dubs]

minimal is OTW 👀

[TheRealFalcon]

Left questions/comments, but nothing blocking

[TheRealFalcon]

So was traceback_texts just not being used before when it was supposed to? If None or a list is passed as ignore_tracebacks, should we just use that use and append to that rather than keeping a separate list here?

[blackboxsw]

Yes traceback_texts was defined and left unused. If False is provided, we want to report any tracebacks. If None is provided, that's the default and in default case I think we want to ignore expected tracebacks per platform. If a list is passed then we should append to that list instead of keeping the separate list here.

[TheRealFalcon]

Nothing that needs to change here, but it does seem a little odd calling verify_clean_boot multiple times in multiple tests in the class given that they're all operating on the same instance and the log won't be any different between tests.

[blackboxsw]

Yeah I had wondered about just consolidating the deprecation test and the no_problems test. I have though consolidated the rsyslog verify_clean_boot call with testy_no_problems case as they are both testing and asserting the same log warning condition based on presence of rsyslogd.

[TheRealFalcon]

LGTM!