Add support for custom HAProxy service config

Allow users to create/override HAProxy service configuration by
copying over '*.cfg' files from {{ node_custom_config
}}/haproxy/services.d/

Ex: /etc/kolla/config/haproxy/services.d/radosgw.cfg

Change-Id: Id84e3b6e62e544582d6917047534e846e026798d
Signed-off-by: Keith Plant <kplantjr@gmail.com>