Automatic merge from submit-queue (batch tested with PRs 51984, 51351, 51873, 51795, 51634)
Revert to using isolated PID namespaces in Docker
**What this PR does / why we need it**: Reverts to the previous docker default of using isolated PID namespaces for containers in a pod. There exist container images that expect always to be PID 1 which we want to support unmodified in 1.8.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes#48937
**Special notes for your reviewer**:
**Release note**:
```release-note
Sharing a PID namespace between containers in a pod is disabled by default in 1.8. To enable for a node, use the --docker-disable-shared-pid=false kubelet flag. Note that PID namespace sharing requires docker >= 1.13.1.
```
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