lighttpd: Add systemd tmpfile to fix lighttpd systemd boot

lighttpd: Add systemd tmpfile to fix lighttpd systemd boot

Problem starting lighttpd application with systemd.

/usr/sbin/lighttpd -D -f /etc/lighttpd/lighttpd.conf
2018-06-22 11:21:34: (server.c.733) opening errorlog '/var/log/lighttpd-error.log' failed: Permission denied
2018-06-22 11:21:34: (server.c.1420) Opening errorlog failed. Going down.

Lighttpd can not write the 'lighttpd-access.log' and 'lighttpd-error.log' files
to the directory '/var/log/'.

When using systemd the directory '/var/log' does not allow the user www-data to
write.

To correct the problem, we add /usr/lib/tmpfiles.d/lighttpd.conf.
This file create the 'lighttpd-access.log' and 'lighttpd-error.log' files  with
the permission

Signed-off-by: Laurent Hartanerot <laurent.hartanerot@atos.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>