convert2rhel Add expected_returncode param to the fixture

expected_returncode defaults to 0, if any other returncode is expected specify the parameter

Jira Issues: RHELC-

Checklist

[ ] PR has been tested manually in a VM (either author or reviewer)
[ ] Jira issue has been made public if possible
[ ] [RHELC-] is part of the PR title
[ ] GitHub label has been added to help with Release notes
[ ] PR title explains the change from the user's point of view
[ ] Code and tests are documented properly
[ ] The commits are squashed to as few commits as possible (without losing data)
[ ] When merged: Jira issue has been updated to Release Pending if relevant

Aug 31 '23 14:08 danmyway

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.08%. Comparing base (d607d64) to head (f328750). Report is 491 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #896   +/-   ##
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  Coverage   94.08%   94.08%           
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  Files          40       40           
  Lines        3889     3889           
  Branches      700      700           
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  Hits         3659     3659           
  Misses        164      164           
  Partials       66       66