iscsi: workaround to let podman read /dev/null

We currently hit this bug: containers/podman#1412
In order to move forward, let's bind-mount /dev/null into the container
until the bug is fixed. Note, it doesn't hurt docker deployment as we
already mounted /dev.

Related-Bug: #1791167
Change-Id: I0e885c248bb08c04fb9b7efa9e075e692879b450

docker/services/iscsid.yaml

@@ -102,6 +102,9 @@ outputs:
                   - /sys:/sys
                   - /lib/modules:/lib/modules:ro
                   - /etc/iscsi:/var/lib/kolla/config_files/src-iscsid:ro
+                  # TODO(emilien) Workaround until this is solved:
+                  # https://github.com/containers/libpod/issues/1412
+                  - /dev/null:/dev/null
             environment:
               - KOLLA_CONFIG_STRATEGY=COPY_ALWAYS
       host_prep_tasks: