Bluetooth-OPP: Synchronize OPP Database cleanup and Shareupdate threads

OPPService threads should be synchronized to avoid race condition.
Otherwise, during incoming file request if bluetooth sub system
retarted due some hardware error and if remote sends the file
immediately bluetooth is recovered application may crash after
accepting the request due to race condition between database cleanup
thread and shareupdate thread.

CRs-Fixed: 767691
Change-Id: Ie7e7bf588f5b8347afed6449898825111c41ae26