Add mcp common scripts repo required for generate model job

We use generate-salt-model-separated-products job
in TryMCP, which is requires to have mcp-common-scripts
repository prepared in gerrit.

Change-Id: Ieca2113a00e216785081b79de91ec6e686e78d30
diff --git a/defaults/init.yml b/defaults/init.yml
index 5679cf9..7b47ac6 100644
--- a/defaults/init.yml
+++ b/defaults/init.yml
@@ -12,6 +12,7 @@
 - system.defaults.rabbitmq
 - system.defaults.debmirror
 - system.defaults.docker_images
+- system.defaults.gerrit
 parameters:
   _param:
     apt_mk_version: stable