Releasing 1.9.1 for VOLTHA-2.9 and updating voltha-protos to 5.1.2

Change-Id: I67698ff9c580315bf56e8d192ed11a44c8685ff8
diff --git a/VERSION b/VERSION
index a5543c6..9ab8337 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.9.1-dev
+1.9.1