988913 - mirror (node) strategy only affect specified repos when units type_id=repository.
docstrings.
correct docstring pertaining to purging orphans.
Merge pull request #543 from pulp/jortel-988913

988913 - mirror (node) strategy only affect specified repos when units type_id=repository.
Merge branch 'pulp-2.2' into pulp-2.2.1