Stub ResourceWithProps instead of GenericResource

Stub ResourceWithProps instead of GenericResource

Stubbing methods in a superclass is an all-or-nothing affair: once a stub
in the subclass is unset, the subclass will no longer inherit changes in
the superclass (i.e. if you then stub out the same method in the
superclass, the subclass will be unaffected).

Previously, we always set the stubs in the superclass (for historical
reasons, to avoid making this change). This would lead to tests that want
to differentiate between types (by stubbing in the derived class)
interfering with the operation of other tests. This patch changes to always
setting the stubs in the derived class.

Change-Id: I2c8dbd22826da14611a6a3f55321f0016446580a