GATT: Fix FD leak caused by GATT profile

Use case: BT ON/OFF with one BLE APP active

Failure: FD leak is observed with ON/OFF stress test
which eventually lead to crash due to unavailability
of FDs.

Steps:
BT ON/OFF with one BLE APP active to retain the
same Bluetooth process ID to check the FD leak issue.

Root Cause: As the Advertisementi manager and Scan
Manager are not cleaning up the looper instances as
part of cleanup, it causes FD leak.

Fix: Cleanup the handler threads in Advertisementmanager
and ScanManager so that there are no resource leaks.

Change-Id: Ia51899f449d57c1ef68a9516b8472d1fd492572b