Set up loaders so that 4.x functions resolve properly

[binford2k]

This will allow the user to test classes using deferred 4.x functions, such as:

class deferred_functions {
  notify { 'message':
    message => Deferred(
                   'inline_epp',
                   [
                     'VAULT_VALUE=<%= unwrap($secret) %>',
                     {'secret'=> Sensitive('a thing') }
                   ]
               )
  }
}

Fixes #782

See https://tickets.puppetlabs.com/browse/PDK-1715 for more info.

Co-authored-by: Josh Cooper joshcooper@users.noreply.github.com

[jpogran]

I think we can ignore the ruby 2.1 travis failure and ticket updating the test matrix

[binford2k]

@jpogran if we do that, then this PR unintentionally drops support for earlier Puppet versions. I should probably update it to load conditionally instead.