Fix finding test data.
Fix finding test data.

ahaberlie/MetPy,ahill818/MetPy,jrleeman/MetPy,Unidata/MetPy,ahaberlie/MetPy,ShawnMurd/MetPy,dopplershift/MetPy,dopplershift/MetPy,Unidata/MetPy,jrleeman/MetPy,deeplycloudy/MetPy