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)
(cherry picked from commit 3369142157ac5b705955b9b8754124c4c24cbd4f)
diff --git a/apache/server/site/gnocchi.yml b/apache/server/site/gnocchi.yml
index 12d5f24..7aaba6f 100644
--- a/apache/server/site/gnocchi.yml
+++ b/apache/server/site/gnocchi.yml
@@ -22,8 +22,7 @@
             port: ${_param:apache_gnocchi_api_port}
           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_gnocchi_log_format}
           wsgi:
             daemon_process: gnocchi-api
             processes: ${_param:gnocchi_api_workers}