tests(slurm_ops): ensure proper file permissions are applied to confi…

…g files

Changes:

- Adds onto `test_config` tests to check the file mode, user, and group of file.
- Fake the user and group by reassigning the `_user` and `_group` to the uid and gid of the user running the tests.
- Redefines constants at the top of the test module so they can be easily found.

Signed-off-by: Jason C. Nucciarone <[email protected]>