Bug 976943 - Add error handing for connect/disconnect process, f=btian, r=gyeh
Bug 976943 - Replace OnConnect/OnDisconnect with one function, f=btian, r=gyeh

In BluetoothProfileController, it's meaningless to separate OnConnect
and OnDisconnect since the following steps would be the same for both
cases. Therefore I introduced a function called NotifyCompletion() for
each profile manager to report the completion of connecting/disconnecting
operations.