Enforce image update from image_to_live.
Enforce image update from image_to_live.

The issue here is if an previous update succeeded but reboot not happen, for what ever unknown reason, this host lost the ability to update again.

I think some of the current update failure in the lab should be caused by this.

Review URL: http://codereview.chromium.org/2031002

coreos/scripts,mjg59/scripts,fivethreeo/scripts,mischief/scripts,smilart/scripts,sigma/coreos-scripts,bcwaldon/coreos-scripts,BugRoger/scripts,vmware/coreos-scripts,gtank/scripts,andrejro/coreos--scripts,vmware/coreos-scripts,zhang0137/scripts,fivethreeo/scripts,crawford/scripts,gtank/scripts,bcwaldon/coreos-scripts,bcwaldon/coreos-scripts,fivethreeo/scripts,mjg59/scripts,mischief/scripts,marineam/coreos-scripts,sigma/coreos-scripts,mischief/scripts,trnubo/scripts,gtank/scripts,zhang0137/scripts,endocode/scripts,crawford/scripts,coreos/scripts,trnubo/scripts,zhang0137/scripts,BugRoger/scripts,vmware/coreos-scripts,mjg59/scripts,andrejro/coreos--scripts,nicescale/scripts,endocode/scripts,smilart/scripts,glevand/coreos--scripts,nicescale/scripts,endocode/scripts,glevand/coreos--scripts,crawford/scripts,andrejro/coreos--scripts,marineam/coreos-scripts,nicescale/scripts,BugRoger/scripts,marineam/coreos-scripts,sigma/coreos-scripts,smilart/scripts,trnubo/scripts