Use absolute path for remaining workflow file operations

[dhalbert]

[Testing #9311]

I did test the artifact and it resolved the problem demonstrated by the test code.py in the original issue, however now I don't think a file can be deleted using web workflow if the folder has been changed from the root folder using os.chdir.

Originally posted by @RetiredWizard in #9311 (comment)

The code change in #9311 also needs to be made in filesystem_for_path() in filesystem.c.