Don't make functional tests inherit from IsolatedUnitTest

There were some functional tests inheriting from IsolatedUnitTest which
doesn't make sense and was causing some issues in newer developments
since IsolatedUnitTest stubs some classes (like Registry's client).

Fixes bug: #1186291

Change-Id: Icafac9edf8b0cec6a96532c609923de2c4d8d6bb