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._
One thing we could do is [namespace](https://github.com/FetLife/rollout#namespacing) by the servers hostname or something so each feature set is managed individually so the keys in redis would look like `node-host-name:feature:tools`. I believe we can get the hostname from [`Socket.gethostname`](http://www.ruby-doc.org/stdlib-1.9.3/libdoc/socket/rdoc/Socket.html#method-c-gethostname) would that be a reliable thing to key off of or can you think of something else?