Add wakelock to UserCallActivity

Add a wakelock to make sure that the phone doesn't go to sleep in the
middle of trying to initiate an outgoing call through Bluetooth (or
something else that doesn't require the screen being on).

Change-Id: Ide945fabbb474cb8ce60fbf704698e566e9f9b01
Fixes: 38328207
Test: manual
2 files changed