RBD add() now returns correct size if given zero

If the RBD store add() is provided with image_size of zero, it
will calculate based on data provided and return the new size.

Change-Id: I06375bcfef7808905b466432e5ca100c942297eb
Closes-bug: 1256044
Remove TestRegistryDB dependency on TestRegistryAPI

TestRegistryDB does not set up the sqlalchemy db it uses with the db models.
These tests only pass when run in conjunction with TestRegistryAPI because that
test case does set up the db. TestRegistryDB should set up the DB as it needs
to.

Fixes bug 1247629

Change-Id: Ib0629634e567e1fb9b98dac50025f5309cd4efec
Merge "RBD add() now returns correct size if given zero"
Merge "Remove TestRegistryDB dependency on TestRegistryAPI"