Allow Bluetooth HAL CAP_SYS_NICE

The Bluetooth HAL has threads that process Bluetooth audio.  They need
to be scheduled as RT priority, so allow the Bluetooth HAL to set its
threads to RT scheduling.

Bug 37518404
Test:  play Bluetooth audio, confirm priority via systrace
Merged-In: I4928cf182a0805c0714e4d073cba15c864fbe328
Change-Id: I4928cf182a0805c0714e4d073cba15c864fbe328

(cherry picked from commit e08303d8)