Modifying tests to run with different configurations

Updated datastore tests to make datastore configurable and not
assume that 'mysql' datastore will always exist.

Fixed test_create_with_bad_availability_zone. Before it was
giving a false positive. Now it is testing the right thing.

Change-Id: Ie4e81e173b73302b40e521e4a41569404203b9d2
Closes-Bug: #1276346
Merge "Modifying tests to run with different configurations"