Automatic merge from submit-queue (batch tested with PRs 55751, 57337, 56406, 56864, 57347). 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>.

Add pod-selector kubectl drain

**Release note**:
```release-note
Added the ability to select pods in a chosen node to be drained, based on given pod label-selector
```

This patch adds the ability to select pods in a chosen node to be drained, based on given pod label-selector. Related downstream issue: https://github.com/openshift/origin/issues/17554

Further, it removes explicit, specific, pod-controller check. The `drain` command currently fails if a pod has a controller of a `kind` [not explicitly handled in the command itself](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubectl/cmd/drain.go#L331). This causes `drain` to be unusable if a node contains pods managed by third-party, or "unknown" controllers.

Based on [this comment](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubectl/cmd/drain.go#L353), the expectation was to fail if a pod's controller was not found for whatever reason. I believe that the `drain` command should not care about the existence of a pod controller. It should only care whether a pod has one, and act according to that controller kind. This solves a downstream bug: https://github.com/openshift/origin/issues/17563

cc @fabianofranz @deads2k @kubernetes/sig-cli-misc