Change saltstack repo class from trusty to xenial

Change-Id: I624b937a5c9db0c614de6ee9d6a756654d597a95
diff --git a/classes/cluster/sl_os_contrail/opencontrail/control.yml b/classes/cluster/sl_os_contrail/opencontrail/control.yml
index dcebe6d..1806c79 100644
--- a/classes/cluster/sl_os_contrail/opencontrail/control.yml
+++ b/classes/cluster/sl_os_contrail/opencontrail/control.yml
@@ -4,7 +4,7 @@
 - system.linux.system.repo.mcp.contrail
 - system.linux.system.repo.mcp.openstack
 - system.linux.system.repo.mcp.extra
-- system.linux.system.repo.saltstack.trusty
+- system.linux.system.repo.saltstack.xenial
 - system.opencontrail.client.resource.edge_router
 - system.opencontrail.control.cluster
 - system.opencontrail.client.cluster