Pin registry image to 2019.2.6

PROD-35836

Change-Id: I1f08eaa961a7ccdefefc57f95aaabde8e8bed212
diff --git a/docker-registry.yml b/docker-registry.yml
index 12cdddf..0380594 100644
--- a/docker-registry.yml
+++ b/docker-registry.yml
@@ -12,7 +12,7 @@
                 replicas: 1
                 restart_policy:
                   condition: any
-              image: docker-prod-local.docker.mirantis.net/mirantis/external/registry:${_param:mcp_version}
+              image: docker-prod-local.docker.mirantis.net/mirantis/external/registry:2019.2.6
               ports:
                 - 15000:5000
               volumes: