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/doc.go

@@ -17,4 +17,4 @@ limitations under the License.
 // Package util implements various utility functions used in both testing and implementation
 // of Kubernetes. Package util may not depend on any other package in the Kubernetes
 // package tree.
-package util
+package util // import "k8s.io/kubernetes/pkg/util"