Remove Mock class monkey patching

Replace use of Mock with Mock(). The Mock class was being modified and
so affecting other tests where Mock is used. An instance of the Mock
class is now used to keep the tests isolated.

Change-Id: Iccab8430d5814258c8c2d1f9af015bce999549bc
Closes-Bug: #1286245
Merge "Remove Mock class monkey patching"