Direct ssh bash output to /dev/null

When using Fedora image the ssh command that executes
netcat doesn't return because stdout remanins open.

Closes-Bug: 1439065
Change-Id: I41a75a5a262ce184cbbb57c39863af3d8f21ad61
diff --git a/tempest/scenario/test_load_balancer_basic.py b/tempest/scenario/test_load_balancer_basic.py
index 0d17048..8f37d74 100644
--- a/tempest/scenario/test_load_balancer_basic.py
+++ b/tempest/scenario/test_load_balancer_basic.py
@@ -185,7 +185,7 @@
             # Start netcat
             start_server = ('while true; do '
                             'sudo nc -ll -p %(port)s -e sh /tmp/%(script)s; '
-                            'done &')
+                            'done > /dev/null &')
             cmd = start_server % {'port': self.port1,
                                   'script': 'script1'}
             ssh_client.exec_command(cmd)