(PUP-1118) Add acceptance test for using directory envs

This checks that an environment that comes from the environmentdir
setting is usable as an environment.
(PUP-1118) Stop using Environment.new

Instead of creating environments directly, we need to go through the
configured environment loaders, otherwise environments can't come from
other places.
(PUP-1118) Fix rdoc1 specs to match changes to rdoc puppet_parser_core

PuppetParserCore was updated to pass environment, known_resource_types;
this just catches up the spec, which runs only on 1.8.7, to match the
changes.
Merge pull request #2306 from zaphod42/feature/master/pup-1118-implement-environment-directory

(PUP-1118) Use directory environments as environments