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/workqueue/doc.go

@@ -23,4 +23,4 @@ limitations under the License.
 //  * Multiple consumers and producers. In particular, it is allowed for an
 //      item to be reenqueued while it is being processed.
 //  * Shutdown notifications.
-package workqueue
+package workqueue // import "k8s.io/kubernetes/pkg/util/workqueue"