Use a CONFDIR variable to show the configured sysconf path in the
generated documentations (html, man pages etc).

Related to:
https://bugzilla.redhat.com/show_bug.cgi?id=1644985



Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20181126105125.30973-1-marcandre.lureau@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>