Stop daemon threads in runtime shutdown

Ensure that daemons are stopped and joins before bringing down the
runtime. This fixes bugs related to native code still running when
we shutdown the runtime.

Also changed the mutex destructor to allow contenders if we are
deleting a monitor lock level mutex.

Bug: 18577101
Change-Id: I6457b35fd69c6997b9003b5f15f39861749843a9