Automatic merge from submit-queue (batch tested with PRs 61644, 61624, 61743, 61019, 61287). 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>.

Added e2e test for local-volume provisioner that does not create PV for discovered non-bind-mounted filesystem.

**What this PR does / why we need it**:

For v2+ of the [local volume provisioner](https://github.com/kubernetes-incubator/external-storage/tree/master/local-volume) non-bind mounted filesystems in a discovery directory will no longer result in local PVs. This change was put in place to handle the non-atomic nature of other methods of adding directories (e.g. https://github.com/kubernetes-incubator/external-storage/issues/482).

This PR tests this change in behavior, and it validates that non-bind mounted directories within a discovery directory do NOT result in a local PV.

**Which issue(s) this PR fixes**:
Fixes https://github.com/kubernetes/kubernetes/issues/61020

**Special notes for your reviewer**:

This test can be executed using the following commands:
```
KUBE_FEATURE_GATES="BlockVolume=true" NUM_NODES=1 go run hack/e2e.go -- --up

go run hack/e2e.go -- --test --test_args='--ginkgo.focus=PersistentVolumes-local.*Local.*volume.*provisioner'
```

If you get the logs from a local volume provisioner pod, you will see the following log messages:
```
$ kubectl logs local-volume-provisioner-94ddb -n e2e-tests-persistent-local-volumes-test-6ls4z
<snip>
I0311 19:01:30.350504       1 controller.go:73] Controller started
E0311 19:01:30.350849       1 discovery.go:172] Path "/mnt/local-storage/notbindmount" is not an actual mountpoint
```


**Release note**:
```release-note
NONE
```