Use openstack_service_workers variable in horizon.conf.j2

Change-Id: I69c94895e4a6f6173363ce818f69344c0fdb22a4

ansible/roles/horizon/templates/horizon.conf.j2

@@ -7,7 +7,7 @@ Listen {{ api_interface_address }}:{{ horizon_port }}
     CustomLog /var/log/kolla/horizon/horizon-access.log combined
 
     WSGIScriptReloading On
-    WSGIDaemonProcess horizon-http processes=5 threads=1 user=horizon group=horizon display-name=%{GROUP} python-path={{ python_path }}
+    WSGIDaemonProcess horizon-http processes={{ openstack_service_workers }} threads=1 user=horizon group=horizon display-name=%{GROUP} python-path={{ python_path }}
     WSGIProcessGroup horizon-http
     WSGIScriptAlias / {{ python_path }}/openstack_dashboard/wsgi/django.wsgi
     WSGIPassAuthorization On