Partition server start/stop in upgrade process

Users would like to be physically present when their servers are being started or stopped to ensure they can fix anything that goes wrong promptly.  However sitting through lengthy data downloads and uploads is not so fun.  This allows them to only be present when servers are starting/stopping.

More context: https://chef.leankit.com/Boards/View/87539983/129913878
CI: http://wilson.ci.opscode.us/job/chef-server-12-trigger-ad_hoc/103/
Same thoughts as the cleanup-only option for the Chef 11 server, but the more I think about it the more I think I'm okay having these settings here.