Automatic merge from submit-queue (batch tested with PRs 47232, 48625, 48613, 48567, 39173)

Include leaderelection in client-go; 

Fix #39117
Fix https://github.com/kubernetes/client-go/issues/28

This PR:
* includes the leaderelection to the staging client-go
* to avoid conflict with golang's testing package, renames package /testing to /testutil, and renames cache/testing to cache/testframework

```release-note
client-go now includes the leaderelection package
```