Upgrade to Omnibus 4.0

Experience tomorrow's future...today. _Act now_ and Releng will throw in one new test platform for __free__.

- [x] Full CI test run: http://wilson.ci.opscode.us/job/chef-server-12-trigger-ad_hoc/204/downstreambuildview/

/cc @opscode/release-engineers @opscode/server-team 

So, if those values are `nil`, will things break? Do they get auto-set when run from test-kitchen?