Merge pull request #421 from pulp/jconnor-928087-pickle-regression

Jconnor 928087 pickle regression
Updating applicability api to accept unit_criteria instead of list of unit keys, updating docstrings and unit tests
Few minor corrections
Merge pull request #423 from pulp/skarmark-928509

Updating applicability api to accept unit_criteria instead of list of unit keys, updating docstrings and unit tests
Merge branch 'tmp-2.1.1' into pulp-2.1
928509 - Platform changes to support override config in applicability
Merge branch 'pulp-2.1'