(PUP-1551) Change environmentdir to environmentpath

In order to provide more flexibility we are changing the
environmentdir setting to an environmentpath setting so that multiple
environment directories can be set as loaders in an established path
sequence.
(PUP-1551) Rename environmentdir acceptance test to environmentpath

And repair some whitespace damage, and a doc typo.
Merge pull request #2320 from jpartlow/feature/master/pup-1551-environmentpath

Feature/master/pup 1551 environmentpath
Merge branch 'master' of https://github.com/puppetlabs/puppet