Use Go canonical import paths

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

Fixes #29014

pkg/util/chmod/doc.go

@@ -16,4 +16,4 @@ limitations under the License.
 
 // Package chown provides an interface and implementations
 // for things that run run the chmod system call.
-package chmod
+package chmod // import "k8s.io/kubernetes/pkg/util/chmod"