ARI: Make bridges/{bridgeID}/play queue sound files

Previously multiple play actions against a bridge at one time would cause
the sounds to play simultaneously on the bridge. Now if a sound is already
playing, the play action will queue playback to occur after the completion
of other sounds currently on the queue.

(closes issue ASTERISK-22677)
Reported by: John Bigelow
Review: https://reviewboard.asterisk.org/r/3379/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@412639 f38db490-d61c-443f-a65b-d21fe96a405b