Bump xos libraries to version 4.0.0

Change-Id: I377de821b6aabf23c5ec5530450e26cd5e6451f5
diff --git a/xos/synchronizer/config.yaml b/xos/synchronizer/config.yaml
index ad6e7e2..411a20f 100644
--- a/xos/synchronizer/config.yaml
+++ b/xos/synchronizer/config.yaml
@@ -15,7 +15,7 @@
 
 
 name: vrouter
-core_version: ">=2.2.1"
+core_version: ">=4.0.0"
 required_models:
   - VRouterService
   - VRouterServiceInstance