Create and track different Handler instances for each Phone.

Phone objects used the same handler in CallManager to
register/unregister callbacks with RIL. This means that, if the
last operation was an unregister, the CallManager would not
be a listener for certain events from the RIL.

Bug: 17414427
Change-Id: I217fad94c64edf479141c1f28f0c1ec8a9e89032