Reorganize startup/shutdown code in SyncManager

* Move all thread-related startup code into run()
* Move all thread-related shutdown code into new method shutdown()
* Add appropriate synchronization during startup/shutdown
* Add thread names to worker threads

Bug; 2645835

Change-Id: Idbd35892cea3de5fbd365102a62103b2f0bdf6c9
Merge (-sours) commit '2b0375b379ca669cedfdccf953195ac3ec23c7a0' into oxygen_4.3

* commit '2b0375b379ca669cedfdccf953195ac3ec23c7a0':
  Reorganize startup/shutdown code in SyncManager