Release the thread_list lock while waiting for daemons.

Daemons might be in a state where they are actually waiting for
it (for example Thread.isInterrupted). If the shutdown thread
doesn't release the lock, such daemon cannot make progress.

bug:27353286
Change-Id: Ib7f4c7d1b56d73a829d01d5bfc0ab663fbb80b46