AudioRecord client threading cleanup

Rename ClientRecordThread to AudioRecordThread to be more similar to
AudioTrack naming.

Only create the thread once, and use resume() and pause() for start()
and stop().  This will allow us to have a known client callback thread
tid that we can pass to AudioFlinger before start().

mActive:
Made mActive a bool not int.
mActive is protected by mLock; volatile is meaningless.
Fixed a few places where mActive was accessed without a lock:
 - stopped()
 - processAudioBuffer()
These aren't used internally, so no need for _l() versions.

Change-Id: I4b8a5c90f3a22d3894b344564cb1c5aef4f1fda2