Alembic migration from revision f44ab9871cd6 to 2eeaf963a447 fails
because the floatingips table doesn't exist.
The fix is to add the plugin to the DB migration path for l3 and ext_gw_mode.
Change-Id: Ic7a9c1d624d2838e9313fa95ed6ddbfea9b6e1c9
Closes-Bug: #1289039