Use Go canonical import paths

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

Fixes #29014

pkg/storage/etcd/util/doc.go

@@ -16,4 +16,4 @@ limitations under the License.
 
 // Package util holds generic etcd-related utility functions that any user of ectd might want to
 // use, without pulling in kubernetes-specific code.
-package util
+package util // import "k8s.io/kubernetes/pkg/storage/etcd/util"