bucket: refactor policies and fix bugs related to enforcing policies. (#2766)

This patch also addresses the problem of double caching at
object layer once at XL and another at handler layer.

cmd/routers.go

@@ -73,10 +73,6 @@ func newObjectLayer(disks, ignoredDisks []string) (ObjectLayer, error) {
 	err = initEventNotifier(objAPI)
 	fatalIf(err, "Unable to initialize event notification.")
 
-	// Initialize and load bucket policies.
-	err = initBucketPolicies(objAPI)
-	fatalIf(err, "Unable to load all bucket policies.")
-
 	// Success.
 	return objAPI, nil
 }