[CT] Fix rebooting logic
[CT] Fix rebooting logic

BUG=skia:

Review URL: https://codereview.chromium.org/1378873003 .

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot