Use Go canonical import paths

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

Fixes #29014

plugin/pkg/auth/doc.go

@@ -15,4 +15,4 @@ limitations under the License.
 */
 
 // Package auth contains implementations for interfaces in the pkg/auth package
-package auth
+package auth // import "k8s.io/kubernetes/plugin/pkg/auth"