Bugfix #2096/#2098 main_v5.0 - fix skip if output exists and do not error if no commands were run

[georgemccabe]

Same changes as PR #2099

Pull Request Testing

• Describe testing already performed for these changes:
  

• Added unit test to confirm bug, then updated logic to get test to pass
• Modified basic use case GridStat.conf and renamed output files to change forecast lead to confirm behavior and confirmed that the fix resolved the issue

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

• Ensure all automated tests pass
• Check that use case that incorrectly skipped runs now behaves as expected
• Check that no errors are reported if no commands are run

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [Yes]

• Will this PR result in changes to the test suite? [No]
  
  New unit tests were added but they should all pass

• Please complete this pull request review by 3/27/2023.
  

Pull Request Checklist

See the METplus Workflow for details.

• Add any new Python packages to the METplus Components Python Requirements table.
• Review the source issue metadata (required labels, projects, and milestone).
• Complete the PR definition above.
• Ensure the PR title matches the feature or bugfix branch name.
• Define the PR metadata, as permissions allow.
  Select: Reviewer(s)
  Select: Organization level software support Project or Repository level development cycle Project
  Select: Milestone as the version that will include these changes
• After submitting the PR, select Development issue with the original issue number.
• After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
• Close the linked issue and delete your feature or bugfix branch from GitHub.

[malloryprow]

This worked great!

03/24 13:34:30.504 metplus (command_builder.py:1008) DEBUG: Skip writing output /scratch1/NCEPDEV/global/Mallory.Row/VRFY/test_METplus/pr_2100/output/grid_stat/grid_stat_2400000L_20200621_120000V*