Make download validation optinal through a new config option.
Merge branch 'master' into rbarlow_optional_validation

Conflicts:
	pulp_rpm/src/pulp_rpm/plugins/importers/iso_importer/configuration.py
	pulp_rpm/test/unit/server/test_iso_importer_configuration.py
	pulp_rpm/test/unit/server/test_iso_importer_sync.py
Merge pull request #121 from pulp/rbarlow_optional_validation

Rbarlow optional validation