(PUP-3341) update apply spec test to make ENC specify env
(maint) prepare apply integration spec for environments
(PUP-3341) prepare apply spec for non-modulepath related tests of environments
(PUP-3341) add tests for the changed behavior

It was decided that (for the time being) puppet apply should behave
like agent/master when an environment is configured (or specified via
command line argument) and prefer the environment that was returned
by the ENC. A warning to that effect should be displayed to the user.

(The warning is not added through this branch - we had this already.)