Release version 2.9.0 for voltha-2.9

Change-Id: I8d36b01a02657d4b282d3990a261d6cb8c392435
diff --git a/VERSION b/VERSION
index ffd8a2b..c8e38b6 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.9.0-dev
+2.9.0