Move few docker_images* under 'defaults' logic

   * Move all docker-images-artifacts under one class
   * This patch affect only:
     - docker-images CI\CD

Change-Id: I534c3a1d642bfb522e4ae8f195906de8f9ee718e
diff --git a/defaults/init.yml b/defaults/init.yml
index 9674799..c27f77c 100644
--- a/defaults/init.yml
+++ b/defaults/init.yml
@@ -11,10 +11,11 @@
 - system.defaults.galera
 - system.defaults.rabbitmq
 - system.defaults.debmirror
+- system.defaults.docker_images
 parameters:
   _param:
-    apt_mk_version: "stable"
-    linux_system_architecture: 'amd64'
+    apt_mk_version: stable
+    linux_system_architecture: amd64
     linux_system_repo_url: "http://mirror.mirantis.com/${_param:apt_mk_version}/"
     # Openstack globals
     openstack_version: 'queens'