VOL-5115 - Create release branch voltha-2.12-beta

VERSION
----------
  o Bump version string to 4.3.7 to avoid future conflicts with the release/patch branch.
  o Suffix *-dev on VERSION string to support non-release development.

Change-Id: I92795c12f9b552adc388809b97bfa8706606cfdd
diff --git a/VERSION b/VERSION
index 4327054..48c3ccc 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-4.3.6
+4.3.7-dev