Fix some synchronization issues. Improve audio job debug output

Fix some synchronization issues. Improve audio job debug output

	* src/media/sound.c (make_audio_job): Always initialie the mutex
	since some sound backends are multi-threaded and will use the
	mutex. Jack and AO are examples.

	* src/media/sound.c (make_audio_job): Improve the job log message.

	* src/media/sound.c (play-media-stream-synchronously): Improve
	play log message to make clear this is synchronous play.

Signed-off-by: Nelson Ferreira <nelson.ferreira@ieee.org>