Add ability for image_to_live to control most of dev_servers abilities.
Add ability for image_to_live to control most of dev_servers abilities.

Before this change, image_to_live could only be used by either passing a custom URL
or using the latest built image.  I've added the following:

- Ability to update from an image.zip
- Ability to update from a specific image.
- Ability to clobber the stateful partition after an update
  (excluding /usr/local and /var)
- Ability to customize and capture both the update and devserver logs.
- Ability to see the progress of an update.

I've also modified the start logic.  It seems the update_engine can get in a state
where if you fail a previous update by killing the devserver, the update engine
will hang for a long time (retries a lot).  So I've changed the behavior of
startup and detecting that the system isn't ready to update, to be, reboot and
then try the update.

BUG=
TEST=Tested with all options.

Review URL: http://codereview.chromium.org/3389009

Change-Id: I9bb42edbf5338385f55db242665c94cd552ab277

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