Enable neutron to work in a multi node setup

On the controller node where devstack is being run should create
the neutron network. The compute node should not.

The the case that we want to run a multi-node neutron setup we need
to configure the following (in the case that a plugin does not
have any agents running on the compute node):
ENABLED_SERVICES=n-cpu,neutron

In addition to this the code did not enable decomposed plugins to
configure their nova configurations if necessary.

This patch ensure that the multi-node support works.

Change-Id: I8e80edd453a1106ca666d6c531b2433be631bce4
Closes-bug: #1613069
diff --git a/lib/neutron b/lib/neutron
index c1552e3..7442efd 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -305,6 +305,9 @@
 
     iniset $NOVA_CONF DEFAULT firewall_driver nova.virt.firewall.NoopFirewallDriver
 
+    # optionally set options in nova_conf
+    neutron_plugin_create_nova_conf
+
     if is_service_enabled neutron-metadata-agent; then
         iniset $NOVA_CONF neutron service_metadata_proxy "True"
     fi