Swap out purely ENV based feature flags for rollout

:fork_and_knife: Implement rollout with features currently enabled by an ENV variable so we may take advantage of some of rollouts more robust features going forward.

_This shouldn't be merged until https://github.com/opscode-cookbooks/supermarket/pull/47 is merged and released._
Makes sense. I'm still wary of performing cluster-wide operations independently from each node, but maybe in practice it won't cause any problems.