Ignore tox -e cover generated files
Ignore tox -e cover generated files

The generated files are like '.coverage.idlerk.5365.021771', which can
not matched by '.coverage'. So change it to '.coverage.*'

Change-Id: Ie0bebceaaa15f2dcf145a708300654f8d3605271

gonzolino/heat,redhat-openstack/heat,openstack/heat,miguelgrinberg/heat,rh-s/heat,maestro-hybrid-cloud/heat,rh-s/heat,miguelgrinberg/heat,dims/heat,maestro-hybrid-cloud/heat,takeshineshiro/heat,srznew/heat,pratikmallya/heat,rdo-management/heat,dragorosson/heat,pshchelo/heat,gonzolino/heat,dims/heat,openstack/heat,dragorosson/heat,redhat-openstack/heat,cryptickp/heat,steveb/heat,cryptickp/heat,rdo-management/heat,NeCTAR-RC/heat,cwolferh/heat-scratch,jasondunsmore/heat,pshchelo/heat,cwolferh/heat-scratch,srznew/heat,NeCTAR-RC/heat,takeshineshiro/heat,ntt-sic/heat,jasondunsmore/heat,pratikmallya/heat,steveb/heat,noironetworks/heat,noironetworks/heat,ntt-sic/heat