Neutron: use "OSC show -f value -c id" instead of "OSC list + grep"

We should leverage server-side filtering.

Change-Id: I3deef791868769b0b7cfc405d73dff57458ca427
diff --git a/exercises/neutron-adv-test.sh b/exercises/neutron-adv-test.sh
index bfd45ec..e8c8f62 100755
--- a/exercises/neutron-adv-test.sh
+++ b/exercises/neutron-adv-test.sh
@@ -156,7 +156,7 @@
 function get_network_id {
     local NETWORK_NAME="$1"
     local NETWORK_ID
-    NETWORK_ID=`openstack network list | grep $NETWORK_NAME | awk '{print $2}'`
+    NETWORK_ID=`openstack network show -f value -c id $NETWORK_NAME`
     echo $NETWORK_ID
 }