Allow to set custom repo via overrides.yml

Update aio and ironic cluster models to allow add custom repo.

Change-Id: Ica43ace3e7e8d5f1e00a8810df6040def90d7bfb
diff --git a/classes/cluster/virtual-mcp11-ovs-ironic/openstack/init.yml b/classes/cluster/virtual-mcp11-ovs-ironic/openstack/init.yml
index fdc0ee5..2cc6792 100644
--- a/classes/cluster/virtual-mcp11-ovs-ironic/openstack/init.yml
+++ b/classes/cluster/virtual-mcp11-ovs-ironic/openstack/init.yml
@@ -90,6 +90,7 @@
     mongodb_ceilometer_password: cloudlab
     mongodb_admin_password: cloudlab
     mongodb_shared_key: eoTh1AwahlahqueingeejooLughah4tei9feing0eeVaephooDi2li1TaeV1ooth
+    linux_system_repo: 'deb [arch=amd64] http://mirror.fuel-infra.org/mcp-repos/ocata/xenial ocata main'
   linux:
     network:
       host: