allow input of stream on unstructured mesh (e.g. mpas)

[mvertens]

Description of changes

This permits use of an unstructured mpas grid as input.

Specific notes

Contributors other than yourself, if any:

CDEPS Issues Fixed: #249
also fixes CTSM Issue ESCOMP/CTSM#2518

Are there dependencies on other component PRs (if so list): No

Are changes expected to change answers: bfb

Any User Interface Changes (namelist or namelist defaults changes):

Testing performed (e.g. aux_cdeps, CESM prealpha, etc):
Verified that with this change cdeps could ingest unstructured input.

Hashes used for testing:

[mvertens]

@uturuncoglu - I think this PR should fix the issue you raised with unstructured meshes.

[uturuncoglu]

@mvertens Thanks. I could try in my end to see what happens. We were trying to use unstructured data to feed ADCIRC ocean component as a part of the UFS Coastal project.