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/limitwriter/doc.go

@@ -16,4 +16,4 @@ limitations under the License.
 
 // Package limitwriter provides a writer that only allows a certain number of bytes to be
 // written.
-package limitwriter
+package limitwriter // import "k8s.io/kubernetes/pkg/util/limitwriter"