Updates to modify_fates_paramfile python script

[ckoven]

Some updates / fixes to modify_fates_paramfile.py script

Description:

A couple fixes/ improvements to modify_fates_paramfile.py.
(1) uses a temporary file so that if something goes wrong during the process the outcome is that no changes are made to any of the files that were initially present.
(2) fixed the logic for scalar parameters; FATES expectation is that they aren't actually scalars but arrays of length 1 and now the tool expects that as well.

Collaborators:

n/a

Expectation of Answer Changes:

None, python tool changes only.

Checklist:

• My change requires a change to the documentation.
• [X ] I have updated the in-code documentation AND wiki accordingly.
• [ X] I have read the CONTRIBUTING document.
• FATES PASS/FAIL regression tests were run
• If answers were expected to change, evaluation was performed and provided

Test Results:

N/A: changes only to python tool so no testing needed

[rgknox]

@ckoven , I can confirm that this PR is safe to the rest of the model. Would you like me to verify the usage of that script, or should we just pull?

[rgknox]

was given the thumbs up