Automatic merge from submit-queue (batch tested with PRs 56217, 56268, 56263, 56328, 56200). 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>.

export ENABLE_POD_PP=true to enable Pod priority and preemption

**What this PR does / why we need it**:
Though pod priority and preemption is disabled by default in Kubernetes 1.8, it too many steps if you want to enable the feature manually. It is important to enable it in `local-up` cluster by `export` variable.

**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 [#](https://github.com/kubernetes/kubeadm/issues/554)

**Special notes for your reviewer**:
cc @shashidharatd @sttts @lavalamp

**Release note**:

```release-note
NONE
```