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._
I get why this block is here, but I wonder if we can accomplish this in some other way. If we're disabling every feature every time the app restarts, we're bound to get reports of a bunch of feature-flagged features disappearing temporarily, since disabling features from one node now disables them across all nodes.