horizon_local_settings.py.j2: adding SECURE_PROXY_ADDR_HEADER

- SECURE_PROXY_ADDR_HEADER is being used to return the clients
      remote address to the logs. On a failed login it is REMOTE_ADDR,
      which will be the loadbalancer address,
      SECURE_PROXY_ADDR_HEADER='HTTP_X_FORWARDED_FOR' makes sure the
      real client IP makes it into the logfiles.
    - https://docs.openstack.org/horizon/latest/configuration/settings.html#secure-proxy-addr-header

Change-Id: I0d68cd4ba7882eb4296a2e4df59afa6582c0303a
(cherry picked from commit d19c9c2cbb)

templates/horizon_local_settings.py.j2

@@ -50,6 +50,7 @@ ALLOWED_HOSTS = [ "{{ horizon_allowed_hosts | join(',') }}" ]
 # For more information see:
 # https://docs.djangoproject.com/en/1.4/ref/settings/#secure-proxy-ssl-header
 SECURE_PROXY_SSL_HEADER = ('{{ horizon_secure_proxy_ssl_header_django }}', 'https')
+SECURE_PROXY_ADDR_HEADER = 'HTTP_X_FORWARDED_FOR'
 {% endif %}
 
 {% if horizon_enable_ssl | bool %}