Introduce container_registry for image prefix

Change-Id: I80067f53aa2b63286b654fff782f0f7b65a2d050
diff --git a/zuul.d/container-images/ovn.yaml b/zuul.d/container-images/ovn.yaml
index 83d4aca..07fa151 100644
--- a/zuul.d/container-images/ovn.yaml
+++ b/zuul.d/container-images/ovn.yaml
@@ -36,21 +36,23 @@
       container_images:
         - context: images/ovn
           registry: harbor.atmosphere.dev
-          repository: harbor.atmosphere.dev/library/ovn-central
+          repository: "{{ container_registry }}/ovn-central"
           arch:
             - linux/amd64
           build_args:
+            - REGISTRY={{ container_registry }}
             - "RELEASE={{ zuul.branch | replace('stable/', '') }}"
             - OVN_COMPONENT=central
           tags:
             - "{{ zuul.branch | replace('stable/', '') }}"
         - context: images/ovn
           registry: harbor.atmosphere.dev
-          repository: harbor.atmosphere.dev/library/ovn-host
+          repository: "{{ container_registry }}/ovn-host"
           arch:
             - linux/amd64
             - linux/arm64
           build_args:
+            - REGISTRY={{ container_registry }}
             - "RELEASE={{ zuul.branch | replace('stable/', '') }}"
             - OVN_COMPONENT=host
           tags: