audiohal: Make closing of effects and streams fast

There were two problems:

1. Joining of reader / writer / process threads (the threads that
   interact with HAL) was taking up to 1 second because the thread
   was usually waiting for an event flag to be toggled, or a 1s
   timeout.

2. Calling IStream.close or IEffect.close shouldn't tax the caller.
   Changed the code so a call to close only signals the thread that
   it's time to exit, and then the thread is only joined in the
   effect or stream destructor.

Bug: 34800063
Bug: 34499806
Test: see repro steps in the bugs
Change-Id: Ife20524a1eba4ec9a78152e89862526e8cd5c960