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/selinux/doc.go

@@ -15,4 +15,4 @@ limitations under the License.
 */
 
 // Package selinux contains selinux utility functions.
-package selinux
+package selinux // import "k8s.io/kubernetes/pkg/util/selinux"