BT: Fix memory leak when BT on & off done many times

Solves a memory leak in BatteryStatsService when Bluetooth
is turn on/off. Solution adds missing close of proxy then
Bluetooth is turned off.

Change-Id: I65f9db298459c7c15f6a10c752992f1d38469445
CRs-Fixed: 476145
Merge branch 'cm-10.1' into martincz