Use Go canonical import paths

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

Fixes #29014

pkg/client/cache/doc.go

@@ -21,4 +21,4 @@ limitations under the License.
 // list currently available nodes), and one that additionally acts as
 // a FIFO queue (for example, to allow a scheduler to process incoming
 // pods).
-package cache
+package cache // import "k8s.io/kubernetes/pkg/client/cache"