Use Go canonical import paths

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

Fixes #29014

pkg/api/doc.go

@@ -21,4 +21,4 @@ limitations under the License.
 // The contract presented to clients is located in the versioned packages,
 // which are sub-directories. The first one is "v1". Those packages
 // describe how a particular version is serialized to storage/network.
-package api
+package api // import "k8s.io/kubernetes/pkg/api"