ARI: Originate to app local channel subscription code optimization.

Reduce the scope of local_peer and only get it if the ARI originate is
subscribing to the channels.

Review: https://reviewboard.asterisk.org/r/3905/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@421009 f38db490-d61c-443f-a65b-d21fe96a405b