Description of problem:

CSI certification tests have a config option `RWX: <boolean>` that enabled tests with ReadWriteMany  volumes (RWX). If the CSI driver supports both block and filesystem volumes, both block and filesystem volumes will be tested with RWX.

We need an opt out (opt in?) to enable only block RWX tests, leaving filesystem tests RWO only. A lot of CSI drivers can attach a block device to multiple nodes and it's a pre-requisite for CNV / KubeVirt, while they can't mount a single ext4 / xfs to multiple nodes. 

There is an old upstream issue with some discussion: https://github.com/kubernetes/kubernetes/issues/105626