Add neutron "segments" plugin to the default list

[1] Added a tests which requires "segments" plugin but
we don't have it enabled in overcloud. It is enabled in
neutron jobs from long[2]. This patch adds this plugin
to the default enabled plugins.

[1] https://review.openstack.org/#/c/558609/
[2] https://review.openstack.org/#/c/459439/

Related-Bug: #1765008
Change-Id: I1bc36c4533dcaadd81d7c93a194e9319217c69cd
(cherry picked from commit bc3600b362)

puppet/services/neutron-base.yaml

@@ -45,7 +45,7 @@ parameters:
         from neutron.core_plugins namespace.
     type: string
   NeutronServicePlugins:
-    default: "router,qos,trunk"
+    default: "router,qos,segments,trunk"
     description: |
         Comma-separated list of service plugin entrypoints to be loaded from the
         neutron.service_plugins namespace.

releasenotes/notes/add_neutron_segments_plugin_to_default-8acb69b112d4b31c.yaml

@@ -0,0 +1,5 @@
+---
+other:
+  - |
+    Add "segments" service plugin to the default list of
+    neutron service plugins.