Merge 2.1.x code changes to master

Following our standard branching process, we need to merge code changes from the 2.1.x branch back to the master branch. I created a ticket for this one b/c I think the next merge-up will involve a fair amount of conflict resolution.

The current PR up for merging stable to master - https://github.com/puppetlabs/puppet-server/pull/540 - would update the master branch to using comidi rather than compojure for routing. We should let that PR land ahead of the work to be done for this ticket. In the process or merging 2.1.x back to master, we'll need to convert the new legacy routes service to using comidi for its routes so that we'll be consistently handling the HTTP metrics that we need to be able to collect per the usage of these routes.