(PUP-3642) Remove environment name from URL path

This commit makes some changes to the indirector network layer
such that the environment name is no longer a part of the main
URL path structure.  This will allow us to have a more finite URL space
and run Puppet in the same webserver with other apps, without
worrying about URL collisions.  Instead, the environment becomes a query
parameter.
TBH, I would rather see all of the query parameters consistently in either the request line or body, as opposed to the `environment` always in the request line, and other parameters in the request line or body. IOW, all params in the body for POST, and on the request line for GET <= 1024, PUT, DELETE, HEAD, OPTIONS.