Ensure Namespace and UID are set in kubelet

Make all kubelet config sources ensure that UID and Namespace are defaulted, if
need be.

We can *almost* disable the "if blank" logic for UID, except for tests that
call APIs that do not run through SyncPods.  We really ought to be enforcing
invariants better.

cmd/integration/integration.go

@@ -622,7 +622,7 @@ func main() {
 			createdPods.Insert(p[:n-8])
 		}
 	}
-	// We expect 5: 2 net containers + 2 pods from the replication controller +
+	// We expect 9: 2 net containers + 2 pods from the replication controller +
 	//              1 net container + 2 pods from the URL +
 	//              1 net container + 1 pod from the service test.
 	if len(createdPods) != 9 {