Enable launching diagnostics from OS broken screen

If firmware diagnostics is enabled allow the user to lauch diagnostics
from the OS broken screen. Currently diagnostics can only be launched
from the recovery screen.

TEST=Tested on arcada device
     make runmisctests

Change-Id: Ic6946338605599ea7411b5658acb2c6fc960a782
Signed-off-by: Mathew King <mathewk@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1564448
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>
3 files changed