[autotest] Backport suite changes to R29.

This merges together the changes to do:
 * remove skip_reimage
 * add priority=priority
 * add timeout=timeout

TEST=None
BUG=None

Change-Id: I678f33dc94c15cda68f30ccbcb8e2cd365dfaf62
Reviewed-on: https://chromium-review.googlesource.com/169184
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
54 files changed