cleanup: use errors.As() in rbd/controllerserver methods
cleanup: use errors.As() in rbd/controllerserver methods

See-also: https://github.com/golang/go/wiki/ErrorValueFAQ#how-should-i-change-my-error-handling-code-to-work-with-the-new-features
Signed-off-by: Niels de Vos <7bda0c0ee7f47171cc808e9e60292cbc5d8140dd@redhat.com>

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