Add support for omega sphere transport tests

[cbegeman]

Add omega support for the sphere_transport test suite

Checklist

• Testing comment in the PR documents testing used to verify the changes

[cbegeman]

Testing

Test suite has been run on chrysalis, intel-impi with omega. All tests fail because they do not meet the order of convergence.

rotation_2d has 1st order convergence
correlated_tracers_2d, divergent_2d and nondivergent_2d do not converge

I will try reducing the omega time step and update this comment. I welcome any additional help on the omega side investigating the tests that do not converge.

[xylar]

@cbegeman, could you post images of the beginning and end states at the highest resolution? It could really be that the centered advection we currently have is not convergent for these more rigorous tracer tests with small-scale tracer or velocity-field structure.

This, in turn, would point to the urgency of higher-order tracer advection that we discussed on Monday.