Fix DB API mismatch with sqlalchemy API

We added a sqlalchemy columns_to_join argument to the
security_group_get_by_name() method, but didn't punch it through
the toplevel DB API. This patch adds that so that they match.

Change-Id: I6fe8d876834036e6fbd79d60f3d7d696d7cf4b83
Merge "Fix DB API mismatch with sqlalchemy API"