Fix stop_neutron metadata agent function

Currently, stop_neutron fails in Jenkins because it kills itself.
This patch ensure we kill only neutron metadata agent, and not the awk
process in itself.

Change-Id: I25d1d90e002fa9eb3c5bc366cc74cb70a2daa69f
Closes-bug: #1269982
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

lib/neutron

@@ -505,8 +505,7 @@ function stop_neutron() {
         [ ! -z "$pid" ] && sudo kill -9 $pid
     fi
     if is_service_enabled q-meta; then
-        pid=$(ps aux | awk '/neutron-ns-metadata-proxy/ { print $2 }')
-        [ ! -z "$pid" ] && sudo kill -9 $pid
+        pkill -9 -f neutron-ns-metadata-proxy
     fi
 
     if is_service_enabled q-lbaas; then