Use Go canonical import paths

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

Fixes #29014

pkg/runtime/doc.go

@@ -42,4 +42,4 @@ limitations under the License.
 // As a bonus, a few common types useful from all api objects and versions
 // are provided in types.go.
 
-package runtime
+package runtime // import "k8s.io/kubernetes/pkg/runtime"