audio policy: reuse direct output when possible

audio policy: reuse direct output when possible

Modified getOutput() logic to not systematically
open a new direct output when a profile matches a request.
This causes a problem when transitioning between two
multichannel tracks as the audio HAL will most of the times
only support one direct output stream open at a time.

Instead, reuse an open output if all the parameters match
or force close the output before reopening it.

Also modify releaseOuput():
- close a direct output only if no client is using it anymore
- call closeOutput() instead of removing the output from
the open output list: this factors in code executed when closing an
output stream.

Bug 8388941

Change-Id: Ic3d3beb21063622ddf57a5b932f93d56f2986f54