[Autotest] Experimental tests should not close the Tree.

Modify run_suites so that aborted experimental tests don't
close the tree.

TEST=Invoked runsuite with -m and a job id of a suite that
     closed the tree because of an experimental failure and
     confirmed that we now pass 'warning'. Also went through
     several local run_suite runs.
BUG=chromium:217750

Change-Id: I45b552ecbbf278eccda96374598d5828d8f07682
Reviewed-on: https://gerrit.chromium.org/gerrit/47839
Commit-Queue: Prashanth Balasubramanian <beeps@chromium.org>
Reviewed-by: Prashanth Balasubramanian <beeps@chromium.org>
Tested-by: Prashanth Balasubramanian <beeps@chromium.org>
1 file changed