Rehome functions to enable Neutron's placement 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: Ib86071881f16de1b69c0f9b1b19b6df8b7e66a07
diff --git a/lib/neutron-legacy b/lib/neutron-legacy
index 7b20a96..b41dfca 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -277,6 +277,7 @@
 source $TOP_DIR/lib/neutron_plugins/services/l3
 
 # Additional Neutron service plugins
+source $TOP_DIR/lib/neutron_plugins/services/placement
 source $TOP_DIR/lib/neutron_plugins/services/trunk
 
 # Use security group or not
@@ -374,6 +375,9 @@
     fi
 
     # Configure Neutron's advanced services
+    if is_service_enabled q-placement neutron-placement; then
+        configure_placement_extension
+    fi
     if is_service_enabled q-trunk neutron-trunk; then
         configure_trunk_extension
     fi