Stop using deprecated --pull-source option

The --pull-source option was deprecated in pike and we're now supposed
to prepend the registry address to the --namespace option.

Moreover the --pull-source option has a bug that causes docker.io
registry to be added twice to the ceph image.

Change-Id: I6acac1826271efcd4d1acf6633bde6eb8a653f44
Closes-Bug: #1724347

roles/overcloud-prep-containers/templates/overcloud-prep-containers.sh.j2

@@ -37,7 +37,7 @@ BUILD_ID={{ docker_image_tag }}
 openstack overcloud container image prepare \
     --images-file {{ working_dir }}/overcloud_containers.yaml \
     {{ prepare_service_env_args }} \
-    --namespace {{ docker_registry_namespace }} \
+    --namespace {{ docker_registry_host }}/{{ docker_registry_namespace }} \
     --tag $BUILD_ID \
 {% if docker_prep_prefix is defined %}
     --prefix {{ docker_prep_prefix}} \
@@ -54,7 +54,6 @@ openstack overcloud container image prepare \
 {% if docker_ceph_tag is defined %}
     --set ceph_tag={{ docker_ceph_tag }} \
 {% endif %}
-    --pull-source  {{ docker_registry_host }} \
     --push-destination {{ local_docker_registry_host }}:8787
 
 openstack overcloud container image upload --verbose --config-file {{ working_dir }}/overcloud_containers.yaml