Creating 1.8 support branch

- Updating .gitreview and Dockerfile

Change-Id: Ibaefc16974c13df0fb94f2c4eb4cc02b779d382f
diff --git a/.gitreview b/.gitreview
index 328aec6..44a6e0e 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,4 +3,4 @@
 port=29418
 project=onos.git
 defaultremote=origin
-defaultbranch=master
+defaultbranch=onos-1.8