(maint) Always use a remote env in the configurer

Before this commit the configurer would track the appropriate environment to
request from the master in the `@environment` variable. This contained simply
the name of the remote environment. The value was passed through to various
indirection requests as the `:environment` parameter. However, as part of
PUP-3244, something changed that caused the configurer to begin failing when
 * The requested environment did not exist remotely
 * There was a cached catalog locally
 * The cached catalog referenced an environment that did not exist
   locally This situation caused the indirector requests to contain an
environment name that the Puppet::Indirector::Request code would then try to
expand into a full environment instance by calling
`Puppet.lookup(:environments).get!(env)`. However, since the environment 
didn't exist locally the `get!` method raised an error.

This commit changes it so that the configurer always converts the
`@environment`, which is always the environment from the server for the 
current run, to `Puppet::Node::Environment.remote`. This stops
`Puppet::Indirector::Request` from trying to load the environment locally.

I don't know how this ever worked...