e2e: set rbd-nbd mounter tests cephLogStrategy to preserve
e2e: set rbd-nbd mounter tests cephLogStrategy to preserve

This is to preserve the rbd-nbd logs post unmap, so that the CI can dump
the available logs from logdir.

Fixes: #2451
Signed-off-by: Prasanna Kumar Kalever <a78d8f98557446023f5b3ba9944d7be259a978a3@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi