Move tests/unit/storage/base under m/tests/storage

If we want third-party backends to inherit from these tests, we need to
ship them along with Marconi. This patch moves storage base tests under
marconi/tests/sotrage.

Implements blueprint refactor-system-tests

Change-Id: Ic7390ead37694bdac9eb341da6f239b8c1178e1e
Merge "Move tests/unit/storage/base under m/tests/storage"