Allow namespace configurability in AudiTestBase

[CuriousVini]

Currently AudiTestBase uses only Default namespace for tests. It would be helpful if AudiTestBase can support namespace configurability. Even if test namespace in AudiTestBase is changed to support namespace configurability, IntegrationTestBase will fail in setUp() due to extra namespace. We should change IntegrationTestBase to allow for changing test namespace. Issue has been filed for this. https://issues.cask.co/browse/CDAP-5564