Generalize RebootStep to ShutdownStep, and add HaltStep.

BUG=None
TEST=Manual

Change-Id: I7ff01b01273d1b723878e5c2db4ca1649a2f917b
Reviewed-on: https://gerrit.chromium.org/gerrit/18341
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Ready: Jon Salz <jsalz@chromium.org>
Tested-by: Jon Salz <jsalz@chromium.org>
2 files changed