VOL-5139 - Create beta-release branch for voltha-onos

VERSION
-------
  o Bump version string for release branch (ver:5.1.5)

.gitreview
----------
  o Assign defaultbranch=voltha-2.12 for the relase branch.

Change-Id: Ia46aa239ba858cb283f6cf672ab11fcf1261c1e7
diff --git a/.gitreview b/.gitreview
index 473a40c..dbac480 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,4 +3,4 @@
 port=29418
 project=voltha-onos.git
 defaultremote=origin
-defaultbranch=master
+defaultbranch=voltha-2.12
diff --git a/VERSION b/VERSION
index b21411a..220d8e0 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.1.5-dev
+5.1.5