Description of problem:

In certain situations, the "pulp" CLI issues warnings on stderr. As the "running pulpcore tasks" check calls the CLI and tries to parse the output (mixing stdout and stderr) as JSON, those warnings make the JSON parser fail and thus failing to detect running tasks
 

How reproducible:

100%
 

Is this issue a regression from an earlier version:

The issue is in new code (introduced in 6.16), so not directly.
It does break upgrades tho, which can be seen as a regression?
 

Steps to Reproduce:

1. Have a system where "pulp status" and friends raise a warning
2. Try to run an upgrade to 6.16

Actual behavior:

--------------------------------------------------------------------------------
Check for running pulpcore tasks:                                     [FAIL]
undefined method `empty?' for nil:NilClass
--------------------------------------------------------------------------------

Expected behavior:

No error.

Business Impact / Additional info:

When you run "pulp" CLI manually, you see a warning like:

#  pulp --format json task list --state-in running --state-in canceling
/usr/lib/python3.11/site-packages/urllib3/connection.py:463: SubjectAltNameWarning: Certificate for foreman.example.com has no `subjectAltName`, falling back to check for a `commonName` for now. This feature is being removed by major browsers and deprecated by RFC 2818. (See https://github.com/urllib3/urllib3/issues/497 for details.)
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Ideally, we'd filter out the stderr and only parse JSON from stdout, but the current code mixes things up and it's a bit complicated to untangle it.