audioflinger: various offload playback fixes

Revert underrun sleep time optimization added for
offload by commit 51716185 which can cause music to pause for a few
seconds in some corner cases.

Allow underruns in STOPPING_1 state to avoid dropping last buffer
received by the AudioTrack callback after stop() is called by the
client.

Allow interruption of thread loop sleep if a command is pending to
speed up track start sequence.

Do not wait for a full AudioTrack buffer before writing to audio HAL
when resuming playback or transitioning to next track.

Also moved log level for underruns in AudioSink from I to D to reduce
spam on user builds.

Bug: 28545177
Bug: 27682362
Bug: 28347796

Change-Id: I05b651b7878a2d2eedcac43cd669e32add171d40