Add log_format variable for apache openstack sites

Add openstack default variables with log formats for apache sites

Aligh log settings with settings from formulas for openstack
services: aodh, barbican, cinder, gnocchi, manila, nova-placement,
panko.

Change-Id: Ie59d341c39e9c50292f4fe28c6227766961d250c
PROD-Related: PROD-28066 (PROD:28066)
diff --git a/apache/server/site/horizon.yml b/apache/server/site/horizon.yml
index 5cfca1e..e909d4c 100644
--- a/apache/server/site/horizon.yml
+++ b/apache/server/site/horizon.yml
@@ -56,8 +56,7 @@
               allow: 'from all'
           log:
             custom:
-              format: >-
-                %v:%p %{X-Forwarded-For}i %h %l %u %t \"%r\" %>s %D %O \"%{Referer}i\" \"%{User-Agent}i\"
+              format: ${_param:apache_site_openstack_horizon_log_format}
             error:
               enabled: true
               level: debug