'Get\'s the room_id and server list for a given room_alias
Args:
room_alias (RoomAlias)
Returns:
Deferred: results in namedtuple with keys "room_id" and
"servers" or None if no association can be found'

@defer.inlineCallbacks
def get_association_from_room_alias(self, room_alias):

    room_id = (yield self._simple_select_one_onecol('room_aliases', {'room_alias': room_alias.to_string()}, 'room_id', allow_none=True, desc='get_association_from_room_alias'))
    if (not room_id):
        defer.returnValue(None)
        return
    servers = (yield self._simple_select_onecol('room_alias_servers', {'room_alias': room_alias.to_string()}, 'server', desc='get_association_from_room_alias'))
    if (not servers):
        defer.returnValue(None)
        return
    defer.returnValue(RoomAliasMapping(room_id, room_alias.to_string(), servers))
