Add a cosine-bell decomposition test

[xylar]

Checklist

• User's Guide has been updated
• Developer's Guide has been updated
• API documentation in the Developer's Guide (api.md) has any new or modified class, method and/or functions listed
• Documentation has been built locally and changes look as expected
• Testing comment in the PR documents testing used to verify the changes
• New tests have been added to a test suite

[xylar]

Testing

I successfully ran the new omega_pr suite on Chrysalis with Intel (with Omega, of course).

I also successfully ran all tests in the cosine_bell suite (convergence_time tests don't pass the analysis step as expected) with MPAS-Ocean on Chrysalis with Intel.

[cbegeman]

I think this looks great! I ran just the icos decomp test on chrys, intel with Omega and it passes

[xylar]

@cbegeman, thanks very much for the review!