Fix rds "promote" command never promoting
Fix rds "promote" command never promoting

Previously, the `promote` command in the `rds` module would always return OK and never actually promote an instance. This was because `promote_db_instance()` had its conditions backwards: if the instance had the `replication_source` attribute indicating that it **was** a replica, it would set `changed = False` and do nothing. If the instance **wasn't** a replica, it would attempt to run `boto.rds.promote_read_replica()`, which would always fail.

thaim/ansible,thaim/ansible