Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
fix README for admission webhook test image
This README is copied from somewhere else and it's out of date.
**Release note**:
```release-note
NONE
```
AdmissionResponse allows mutating webhook to send apiserver a json patch
to mutate the object.
This reflects the imperative nature of AdmissionReview. It adds
AdmissionRequest and AdmissionResponse in place of status/spec.
The AdmissionResponse the allows the mutating webhook
to send back a json path with the mutated version of the requested
object.
Fixed the integration test to clean up properly.
Switched test image to 1.8v5 to reflect API changes.
Make sure to cache test framework client for cleaup test code.
Switched to pointer for patch type.
Factored in @liggitt's feedback.
Factored in @lavalamp's feedback.
