Solve potential race condition on known_hosts file when executing
scripts in parallel

Change-Id: I4b1eb76a79d978a9241cd08df49d9ed87e90cdc3
diff --git a/tools/test/bin/onos-all b/tools/test/bin/onos-all
index 6d5617d..e7d8031 100755
--- a/tools/test/bin/onos-all
+++ b/tools/test/bin/onos-all
@@ -24,5 +24,5 @@
 
 for node in $nodes; do
   echo "Issuing command on $node.."
-  ssh -p 8101 -o StrictHostKeyChecking=no $node "$@"
+  ssh -q -p 8101 -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null $node "$@"
 done