CRAS: dbus_control - Add serial number for USB device for stable id

Get additional sys attribute for "serial" which is serial number in
udev.
Add it into the stable_id_new calcuation and keep stable_id for backward
compitable.

BUG=chromium:661861
TEST=Plug 2 same type USB speakers into chromebook.
  execute
  "dbus-send --system
  --type=method_call
  --print-reply
  --dest=org.chromium.cras
  /org/chromium/cras
  org.chromium.cras.Control.GetNodes"

  Check if we have the same stable_id but different stable_id_new for the 2
  speakers.

  pass make check for unit test.

Change-Id: Iefefe383fd6143dd7c28fdba3cf3f3872c2dd726
Reviewed-on: https://chromium-review.googlesource.com/407723
Commit-Ready: Hsu Wei-Cheng <mojahsu@chromium.org>
Tested-by: Hsu Wei-Cheng <mojahsu@chromium.org>
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
16 files changed