Add battery indicator to bluetooth icon

This cl change util method in bluetooth package to return
drawable instead of resId.

If the bt device has battery level, then method return customized
layerDrawable, otherwise return a simple drawable created from
resId.

Bug: 63393322
Test: RunSettingsRoboTests

Change-Id: Ib21822eafda0e8570212ce5cb070478e4f4876a2
Merged-In: Ib21822eafda0e8570212ce5cb070478e4f4876a2