support running landice/greenland/mesh_gen test case on workstations

[cwsmith]

This PR passes the parallel_executable to a few functions that were hardcoded to use srun. With the right input files, this allows testing on workstations with limited memory and cores.

Testing was done with subsampled GIS inputs (to 4km, thanks to @matthewhoffman) for the landice/greenland/mesh_gen test.

Checklist

• User's Guide has been updated - no change needed
• Developer's Guide has been updated - no change needed
• API documentation in the Developer's Guide (api.rst) has any new or modified class, method and/or functions listed - no changes needed - the doc string for interp_gridded2mali was updated in compass/landice/mesh.py
• Documentation has been built locally and changes look as expected - the new parallel_executable arg is rendered in the html
• not applicable The E3SM-Project submodule has been updated with relevant E3SM changes
• not applicable The MALI-Dev submodule has been updated with relevant MALI changes
• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes
• not applicable? New tests have been added to a test suite