Clean up brillo_audio_test.

Makes the following changes to brillo_audio_test:
  - Accept duration, format, number of channels, and sample rate as
    arguments.
  - Uses base::FlagHelper to parse command line arguments.
  - Removes play_multiple option.
  - Replaces printfs with LOGs.
  - Updates README to use markdown.
  - General cleanup.

BUG=26692283
TEST=brillo_RecordingAudioTest & brillo_PlaybackAudioTest pass for both
     stagefright and libmedia

Change-Id: I011750d7ff4f7fa586b191c2c9f327fc07fc4e41
12 files changed