music resumes playback after first call hungup and second call on hold

[Bill Filler]

krillin rtm build 208

Steps to reproduce:

1) open music app and play some music through the speaker
2) call ubuntu phone
3) answer call
4) the music is paused correctly
5) call ubuntu phone from another phone
6) answer the second call (the first call is automatically put on hold)
7) hangup the second call

Expected results:
- the first call is still connected but on hold, no music should be playing
- music should not be resumed until all calls are disconnected

Actual results:
- the first call is still connected on hold, but music is now playing through the earpiece (not speaker)
- after un-holding the first call you can hear a mix of the audio from the callers voice and the music
- when hang up the call the music switches from the earpiece to the speaker

[Ricardo Salveti (rsalveti)]

In media-hub we need to add an additional logic to only resume if there is no active calls.