Use set horizon log filename to original

Map.jinja from horizon formula:
   'apache_log_dir': '/var/log/apache2',
   'apache_log_filename': 'openstack_dashboard',

Change-Id: I47e2810a564dc5ab5dcbdf710d18f68b5ebf28a6
PROD-related: PROD-33543
diff --git a/apache/server/site/horizon.yml b/apache/server/site/horizon.yml
index e909d4c..2c85f6b 100644
--- a/apache/server/site/horizon.yml
+++ b/apache/server/site/horizon.yml
@@ -57,6 +57,7 @@
           log:
             custom:
               format: ${_param:apache_site_openstack_horizon_log_format}
+              file: '/var/log/apache2/openstack_dashboard_access.log'
             error:
               enabled: true
               level: debug