Fix default branch for 1.15

Change-Id: I9446f40b87f56449c489dde5186d9f24e09664dc
diff --git a/.gitreview b/.gitreview
index c24bb9d..7a36c63 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,4 +3,4 @@
 port=29418
 project=OnosSystemTest.git
 defaultremote=origin
-defaultbranch=master
+defaultbranch=onos-1.15