Bug 1049089 - Speed up selinux labeling usage

* Stop resetting selinux context n-times on same code path
* Stop creating selinux labels when they are not needed
* Expose chcon rather than shelling out to restorecon(1)

Conflicts:
	node/lib/openshift-origin-node/model/v2_cart_model.rb
Merge pull request #4655 from jwhonce/bug/1049089

Merged by openshift-bot