rbd: fix snapshot id idempotency issue
rbd: fix snapshot id idempotency issue

This commit fixes snapshot id idempotency issue by
always returning an error when flattening is in progress
and not using `readyToUse:false` response.

Signed-off-by: Rakshith R <2c7b05ed1488c7110901626c2c56645675e22767@redhat.com>

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