This updates the HPA controller to use the polymorphic scale client from
client-go. This should enable HPAs to work with arbitrary scalable
resources, instead of just those in the extensions API group (meaning we
can deprecate the copy of ReplicationController in extensions/v1beta1).
It also means that the HPA controller now pays attention to the
APIVersion field in `scaleTargetRef` (more specifically, the group part
of it).
Note that currently, discovery information on which resources are
available where is only fetched once (the first time that it's
requested). In the future, we may want a refreshing discovery REST
mapper.
Automatic merge from submit-queue (batch tested with PRs 51416, 53535). 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>.
PodSecurityPolicy: teach fuzzer about fsGroup/supplementalGroups strategies
**What this PR does / why we need it**:
At present, fuzzer for PSP doesn't take into account `fsGroup`/`supplementalGroups` strategies. This PR teach fuzzer about these strategies in order to have ability to catch more possible errors.
**Special notes for your reviewer**:
Let me know if you think that we need to cover more (all?) fields in the PSP.
**Release note**:
```release-note
NONE
```
PTAL @pweil- @sttts
CC @simo5
Solly Ross