Fix check_cmd behavior for file.managed state

Resolves #16926.

I'd like to get some additional eyes on this as I am not 100% sure that this is
the correct fix. I haven't done anything with mod_run_check_cmd before. The one
major change that I made was to change the 'result' key in the dict returned by mod_run_check_cmd to ``False``. The reason for this was because when I ran using a check_cmd of ``/bin/false``, I would get a True state result, with a comment of "check_cmd execution failed".