Receive phone call, sound via BT speaker by default.

[Hannah Zhu]

Information:
phablet@ubuntu-phablet:~$ system-image-cli -i
current build number: 63
device name: krillin
channel: ubuntu-touch/rc/bq-aquaris.en
last update: 2016-09-05 13:29:03
version version: 63
version ubuntu: 20160903
version tag: OTA-13-rc
version device: 20160606-ab415b2
version custom: 20160831-991-38-18

https://prod.practitest.com/p/1548/qtest_runs/5967362/edit

Precondition:
Connect BT speaker with phone.

Step:
1. Call DUT from secondary phone.
2. Receive the phone call
3. Check the sound icon is via BT speaker by default, but the BT speaker isn't support to voice call.

Expect result:
The call should use phone by default, not the BT speaker.