audio: Modify CRAS ALSA plugin to control current node's volume.

Based on #1053 (test fails otherwise).

Already merged upstream (https://chromium-review.googlesource.com/#/c/218941/).

Also, patch does not apply cleanly before R31/4731, so we change the minimum version to that (published to stable around December 2013). (actually, I think the check should be much tighter than this, but we need to update the message to something less scary)

Tested in `2014-09-23_01-47-09_drinkcat_chroagh_audio-volume-fix_-R_precise_30`.