Automatic merge from submit-queue (batch tested with PRs 62748, 60536, 62300, 62661, 62731). 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>.
Instrument transformer.go with latency metrics.
**What this PR does / why we need it**:
Instrument transformer.go with latency metrics - allowing to measure performance impact of adding KMS Providers.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
"NONE"
```
Add a smoke test that checks for the existence of some representative
paths from the apiextensions-server and the kube-aggregator server,
both part of the delegation chain in kube-apiserver.
abstract out etcd server creation
test/integration/framework: cleanup master_utils.go
kube-apiserver: move StartTestServer tests into test/integration/master
Fix the failing scale test
kube-apiserver's TestServer now returns a struct instead of individual values
