Fix an error message in the neutron script

The $PHYSICAL_NETWORK in the error message should be
$PRIVATE_NETWORK_NAME, because the command just before this error
message refers to $PRIVATE_NETWORK_NAME.

Change-Id: I9a648f8bd0e61abde8e93bc08282c14b35ec06bd
diff --git a/lib/neutron b/lib/neutron
index 15a5f00..8d27feb 100755
--- a/lib/neutron
+++ b/lib/neutron
@@ -552,7 +552,7 @@
         sudo ip link set $PUBLIC_INTERFACE up
     else
         NET_ID=$(neutron net-create --tenant-id $TENANT_ID "$PRIVATE_NETWORK_NAME" | grep ' id ' | get_field 2)
-        die_if_not_set $LINENO NET_ID "Failure creating NET_ID for $PHYSICAL_NETWORK $TENANT_ID"
+        die_if_not_set $LINENO NET_ID "Failure creating NET_ID for $PRIVATE_NETWORK_NAME $TENANT_ID"
 
         if [[ "$IP_VERSION" =~ 4.* ]]; then
             # Create IPv4 private subnet