Remove test falkiness

This test injects an actual Resource object, this can lead to
variability depending on form factor.
Resources need to be overridden, and parameters should be properly
mocked so behavior is predictable.

Test: atest MediaHierarchyManagerTest
Fixes: 211048996
Change-Id: I687436c70f7a08ac0e13e086020a41932f3e0562