Add tests for baroclinic and barotropic potential vorticity.
Add tests for baroclinic and barotropic potential vorticity.

dopplershift/MetPy,jrleeman/MetPy,ahaberlie/MetPy,Unidata/MetPy,ahaberlie/MetPy,jrleeman/MetPy,Unidata/MetPy,dopplershift/MetPy,ShawnMurd/MetPy