Don't set tempest fixed_network_name with neutron

If neutron is enabled then there isn't a shared private network
between all tenants which is what is required for the
fixed_network_name config option. This commit adds a conditional
to not set that option when neutron is enabled. While not necessarily
fatal to tempest it does emit a warning on almost every server create
call if it is set with a non-existent network name.

Change-Id: I1a42fa6b0b5a93b411c08ec35df043d6ea69d453
diff --git a/lib/tempest b/lib/tempest
index 9c22716..f02b0d1 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -344,7 +344,7 @@
     iniset $TEMPEST_CONFIG compute flavor_ref $flavor_ref
     iniset $TEMPEST_CONFIG compute flavor_ref_alt $flavor_ref_alt
     iniset $TEMPEST_CONFIG compute ssh_connect_method $ssh_connect_method
-    if ! is_service_enabled n-cell; then
+    if [[ ! $(is_service_enabled n-cell) && ! $(is_service_enabled neutron) ]]; then
         iniset $TEMPEST_CONFIG compute fixed_network_name $PRIVATE_NETWORK_NAME
     fi