factory_install_service: Fix find_best_tty result to include /dev/ path.

The find_best_tty should return a full device path instead of console node name
(the kernel command line provides only node name).

BUG=chrome-os-partner:33168
TEST=Boots on headless device and see proper console.

Change-Id: I013af6a90219fde5c2aba7e0d09cd703d04fd4e8
Reviewed-on: https://chromium-review.googlesource.com/255344
Reviewed-by: Mao Huang <littlecvr@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Hung-Te Lin <hungte@chromium.org>
1 file changed