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/config/doc.go

@@ -17,4 +17,4 @@ limitations under the License.
 // Package config provides utility objects for decoupling sources of configuration and the
 // actual configuration state. Consumers must implement the Merger interface to unify
 // the sources of change into an object.
-package config
+package config // import "k8s.io/kubernetes/pkg/util/config"