Mark a failing test on Windows/Appveyor as xfail
Mark a failing test on Windows/Appveyor as xfail

It appears the Python DLLs in created (Conda) environments stay in use
when run on Windows/Appveyor, so that removing the environments fails
and their re-creation cannot be tested.  Does not occur on all Windows
platoforms, however, and adding sleeps does not seem to resolve it.

qwhelan/asv,spacetelescope/asv,mdboom/asv,airspeed-velocity/asv,waylonflinn/asv,airspeed-velocity/asv,mdboom/asv,pv/asv,edisongustavo/asv,waylonflinn/asv,qwhelan/asv,giltis/asv,spacetelescope/asv,pv/asv,spacetelescope/asv,edisongustavo/asv,qwhelan/asv,mdboom/asv,airspeed-velocity/asv,pv/asv,giltis/asv,giltis/asv,qwhelan/asv,mdboom/asv,waylonflinn/asv,spacetelescope/asv,edisongustavo/asv,pv/asv,airspeed-velocity/asv