Tweaks for running the container registry in k8s (#760)

Minor tweaks for running the container-registry in k8s.  The big change is not requiring --image-registry.

Reviewed-on: https://git.vdb.to/cerc-io/stack-orchestrator/pulls/760
Reviewed-by: David Boreham <dboreham@noreply.git.vdb.to>

stack_orchestrator/data/compose/docker-compose-container-registry.yml

@@ -5,9 +5,11 @@ services:
     environment:
       REGISTRY_LOG_LEVEL: ${REGISTRY_LOG_LEVEL}
     volumes:
+      - config:/config:ro
       - registry-data:/var/lib/registry
     ports:
       - "5000"
 
 volumes:
+  config:
   registry-data:

stack_orchestrator/deploy/deployment_create.py

@@ -327,12 +327,14 @@ def init_operation(deploy_command_context, stack, deployer_type, config,
     default_spec_file_content = call_stack_deploy_init(deploy_command_context)
     spec_file_content = {"stack": stack, constants.deploy_to_key: deployer_type}
     if deployer_type == "k8s":
-        if kube_config is None:
-            error_exit("--kube-config must be supplied with --deploy-to k8s")
-        if image_registry is None:
-            error_exit("--image-registry must be supplied with --deploy-to k8s")
+        if kube_config:
             spec_file_content.update({constants.kube_config_key: kube_config})
+        else:
+            error_exit("--kube-config must be supplied with --deploy-to k8s")
+        if image_registry:
             spec_file_content.update({constants.image_registry_key: image_registry})
+        else:
+            print("WARNING: --image-registry not specified, only default container registries (eg, Docker Hub) will be available")
     else:
         # Check for --kube-config supplied for non-relevant deployer types
         if kube_config is not None: