Merge branch '2.6.x' into next

* 2.6.x: (36 commits)
  Updated CHANGELOG for 2.6.7rc1
  (#5073) Download plugins even if you're filtering on tags
  Fix #5610: Prevent unnecessary RAL lookups
  Revert "Merge branch 'ticket/2.6.x/5605' of git://github.com/stschulte/puppet into 2.6.next"
  (#6723) Fix withenv environment restoration bug
  (#6689) Remove extraneous include of Puppet::Util in InventoryActiveRecord
  Remove extra trailing whitespace from lib/puppet/resource.rb
  (#5428) More fully "stub" Puppet::Resource::Reference for use with storedconfigs
  (#6707) Fix typo in rest_authconfig.rb
  (#6689) Make inventory_active_record terminus search quickly
  (#5392) Give a better error when realizing a non-existant resource
  (#2645) Adding a less-stubby test to verify the "system" attribute's behavior
  Update CHANGELOG for 2.6.6
  maint: Remove serialization of InventoryFact values
  maint: Rename InventoryHost to InventoryNode
  Fixed #2645 - Added support for creating system users
  maint: Remove spec run noise
  maint:Refactor of mount provider integration tests
  (#6338) Support searching on metadata in InventoryActiveRecord terminus
  (#6338) Implement search for InventoryActiveRecord facts terminus
  ...

This merge includes essentially reverting #4904's change to the mount
type since tests that came in from 2.6.x specified different
behavior and what's correct is not clear to me.  I've reopened #4904 and
added it to our backlog, and talked to Nigel about the RFC that's
currently out on the puppet-users mailing list for a bigger refactor of
how the mount provider works.

Manually Resolved Conflicts:
    spec/spec_helper.rb
    spec/unit/indirector/queue_spec.rb