Clearing cell environment before borrowing and after returning cell.

Change-Id: Ia8da10406a25e9687cef5d7f8e31e9ceb11d8af9
diff --git a/utils/warden/bin/cell-def b/utils/warden/bin/cell-def
index badad59..b923707 100755
--- a/utils/warden/bin/cell-def
+++ b/utils/warden/bin/cell-def
@@ -15,3 +15,5 @@
 echo "export ONOS_USER=sdn"
 echo "export ONOS_USE_SSH=true"
 echo "export ONOS_APPS=${apps}"
+echo "export ONOS_WEB_USER=onos"
+echo "export ONOS_WEB_PASS=rocks"