Update to onosproject/onos:latest

Change-Id: If62064c740ac2da26ed06bc710830faf82ae9729
diff --git a/roles/onos-vm-install/files/fabric-docker-compose.yml b/roles/onos-vm-install/files/fabric-docker-compose.yml
index 5ad7f3d..a7713bf 100644
--- a/roles/onos-vm-install/files/fabric-docker-compose.yml
+++ b/roles/onos-vm-install/files/fabric-docker-compose.yml
@@ -4,7 +4,7 @@
 services:
 
    xos-onos:
-      image: onosproject/onos:1.6
+      image: onosproject/onos:latest
       expose:
       - "6653"
       - "8101"