Move duplicated ring middleware into common library

https://github.com/puppetlabs/trapperkeeper-status/blob/master/src/puppetlabs/trapperkeeper/services/status/ringutils.clj, https://github.com/puppetlabs/pe-file-sync/blob/master/src/clj/puppetlabs/enterprise/ringutils.clj, and https://github.com/puppetlabs/puppet-server/blob/master/src/clj/puppetlabs/puppetserver/ringutils.clj contain a lot of duplicate ring middleware code.

This should be moved out into a common library (possibly https://github.com/puppetlabs/ring-middleware/?)