tests: factorize patchable attribute testing
tests: factorize patchable attribute testing

This is a factorization in order to introduce different patchable
attributes for each resource type.

Change-Id: I886a7e18bb14e6a026cf5280e28b5d670ef3d152

idegtiarov/gnocchi-rep,sileht/gnocchi,sileht/gnocchi,idegtiarov/gnocchi-rep,idegtiarov/gnocchi-rep,leandroreox/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi,gnocchixyz/gnocchi