[autotest] Move to restarting the UI using upstart, by default

The contract between Chrome and the session manager wrt signing out is
changing, again.  As such, we're going to make StopSession either
behave differently or go away.  So, to restart the UI during a test,
let's just use the upstart 'restart ui' command.

BUG=chromium-os:21877
TEST=suite_Smoke and login_*Ownership*
STATUS=Verified

Change-Id: Ib1afb0dfe5bd7276df9220b61df2c6a4a4661e86
Reviewed-on: http://gerrit.chromium.org/gerrit/10512
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
Commit-Ready: Chris Masone <cmasone@chromium.org>
3 files changed