Rehome functions to enable Neutron's segments integration

Those functions were part of the neutron devstack plugin but we
discussed it during last PTG [1] and decided to move to the Devstack
repo as plugins which are used by e.g. CI jobs which are defined outside
of the neutron repository.
Placement integration is used e.g. in the tempest-slow job which is
defined in tempest and used by many different OpenStack projects.

[1] https://etherpad.opendev.org/p/neutron-yoga-ptg#L142

Change-Id: I2c26063896ab2679cffd01227a40a3283caa3b17

lib/neutron

@@ -294,6 +294,7 @@ source $TOP_DIR/lib/neutron_plugins/services/l3
 source $TOP_DIR/lib/neutron_plugins/services/placement
 source $TOP_DIR/lib/neutron_plugins/services/trunk
 source $TOP_DIR/lib/neutron_plugins/services/qos
+source $TOP_DIR/lib/neutron_plugins/services/segments
 
 # Use security group or not
 if has_neutron_plugin_security_group; then
@@ -416,6 +417,10 @@ function configure_neutron {
             configure_l3_agent_extension_gateway_ip_qos
         fi
     fi
+    if is_service_enabled neutron-segments; then
+        configure_placement_neutron
+        configure_segments_extension
+    fi
 
     # Finally configure Neutron server and core plugin
     if is_service_enabled q-agt neutron-agent q-svc neutron-api; then

lib/neutron_plugins/services/segments

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+function configure_segments_service_plugin {
+    neutron_service_plugin_class_add segments
+}
+
+function configure_segments_extension {
+    configure_segments_service_plugin
+}
+