Support in image_to_live.sh for UI jank investigation.
Support in image_to_live.sh for UI jank investigation.

We need to update image_to_live.sh to run in a loop to help investigate
the kernel behavior during AU. Update_engine_client now allows a new
option to reset the state of update_engine so that update_engine can
repeatedly apply updates without requiring a reboot in between.

This CL simply runs the existing functionality in a loop, with the
additional step of calling update_engine_client each time to reset the
state of update_engine to idle.

BUG=chromium-os:27954
TEST=Tested on ZGB.
CQ-DEPEND=I561e58893818a1b4990fdc131cd3bb64e473155e
Change-Id: I13e958713af64d1f8c44b373e0a16886999e377b
Reviewed-on: https://gerrit.chromium.org/gerrit/29911
Commit-Ready: Jay Srinivasan <ea9e5a30f2916c6637fa6ca08ecf7ee1a6ef3e54@chromium.org>
Reviewed-by: Jay Srinivasan <ea9e5a30f2916c6637fa6ca08ecf7ee1a6ef3e54@chromium.org>
Tested-by: Jay Srinivasan <ea9e5a30f2916c6637fa6ca08ecf7ee1a6ef3e54@chromium.org>

mgireesh05/dev-util,marineam/coreos-dev-util,marineam/coreos-dev-util,coreos/dev-util,mgireesh05/dev-util,mgireesh05/dev-util,coreos/dev-util,coreos/dev-util