Reduced the impact of "synchronized" statements

* Removed "synchronized" statements that are not needed
* Replaced "synchronized" statements with Read/Write lock as
 appropriate. The lock protects the access to and the setting of
 BluetoothAdapter.mService and BluetoothManagerService.mBluetooth and
 associated state.

Bug: 28734075
Bug: 28799467
Change-Id: I8f8281c505f0a1ae0add1e14a3caba1f5b2a98e4