(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.
@rlinehan I'm not thrilled about how deep into implementation details this test has to go in this incarnation, but between the mocking that is going on in these tests and the somewhat complex implementation of the `query` method on the Webrick `HTTPRequest` class, I couldn't think of a better way to code up this test.  If you have any ideas let me know!