QuantumDbPluginV2 should have db connection string configurable

    def __init__(self):
        # NOTE(jkoelker) This is an incomlete implementation. Subclasses
        # must override __init__ and setup the database
        # and not call into this class's __init__.
        # This connection is setup as memory for the tests.
        sql_connection = 'sqlite:///:memory:'
        db.configure_db({'sql_connection': sql_connection,
                         'base': models_v2.model_base.BASEV2})