Use Go canonical import paths

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

Fixes #29014

pkg/apis/rbac/doc.go

@@ -17,4 +17,4 @@ limitations under the License.
 // +k8s:deepcopy-gen=package,register
 
 // +groupName=rbac.authorization.k8s.io
-package rbac
+package rbac // import "k8s.io/kubernetes/pkg/apis/rbac"