Use Go canonical import paths

Add canonical imports only in existing doc.go files.
https://golang.org/doc/go1.4#canonicalimports

Fixes #29014

pkg/types/doc.go

@@ -15,4 +15,4 @@ limitations under the License.
 */
 
 // Package types implements various generic types used throughout kubernetes.
-package types
+package types // import "k8s.io/kubernetes/pkg/types"