TestCaseBase should inherit from unittest.TestCase

All classes in the test aspect class heirachy should inherit
from unittest.TestCase.

Fixing this slightly changes the MRU, but otherwise has no effect.
It does allow better static and dynamic checking of the code.

Change-Id: I3a3c857c3a26bf70262926062d1e9f032a648ee9
Merge "TestCaseBase should inherit from unittest.TestCase"