Moving to ONOS 2.5.7-rc1 to incorporate persistent mastership

Change-Id: If3f7670dfa08be8507f39082e3745c4e6dc07eae
diff --git a/VERSION b/VERSION
index 6149d55..102f7a5 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.1.0-dev4
+5.1.0-dev5