HFP should let the system handle ringtones

https://www.youtube.com/watch?v=NJVrTYbxwgA

First of all, it was choosing the sound in this order:

1. alarm sound
2. notification sound
3. ringtone sound

me: o_O

Second of all, it can't take custom ringtones
for contacts into account.

Change-Id: I16e04e69bdc9b190f8d12412dfd8365420f1da5b