Automatic merge from submit-queue (batch tested with PRs 47806, 49539, 48763, 47049, 50600). 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>..

flexvolume: remove a mount directory in a error case

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

flexVolumeMounter.SetUpAt creates a directory, where a volume has to be
mounted, and we have to remove this directory in a error case. Otherwise
we see errors like this:

Orphaned pod 673b66d9-70f7-11e7-a5fa-525400307392 found, but volume paths are still present on disk

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

https://github.com/kubernetes/kubernetes/issues/49383

**Special notes for your reviewer**:

**Release note**:

Fix a rollback code for the flexvolume mount operation