Automatic merge from submit-queue (batch tested with PRs 49444, 47864, 48584, 49395, 49118)
Allow unmounting bind-mounted directories.
**What this PR does / why we need it**:
For files, we cannot use `path/..`;
we could use `filepath.Dir` but for bind-mounted, `isNotMounted` which calls `IsLikelyNotMountPoint` would not work anyway.
Let's just have the driver do the work.
Addressing
```
Error: UnmountVolume.TearDown failed for volume "..." (volume.spec.Name: "...") pod "..." (UID: "...") with: lstat /path/.../test-flex/..: not a directory
```
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
N/A
**Special notes for your reviewer**:
N/A
**Release note**:
```release-note
It is now posible to use flexVolumes to bind mount directories and files.
```
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