Enable swift by default.

- Set by default SWIFT_REPLICAS to 1 since this is the most common use
  case when using it in devstack.
- If we have swift_replicas to 1 launch the object container account and
  proxy servers in foreground in screen.
- Allow any s- services if we have just 'swift' in service enabled
  instead of having to specify all s- services to enable swift. This will be
  removed in the future.

Change-Id: I496f79e14f99bd7e9f2c7deee12a4b6e935c3a5b
Merge "Enable swift by default."