Refuse to daemonize when running from systemd

Refuse to daemonize when running from systemd

We start with systemd Type=notify, so refuse to daemonize. This does not
affect starting openvpn from script or command line.

v2: Update commit message about script and command line.

Signed-off-by: Christian Hesse <mail@eworm.de>
Tested-By: Richard Bonhomme <fragmentux@gmail.com>
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <20161201213104.5667-2-list@eworm.de>
URL: http://www.mail-archive.com/search?l=mid&q=20161201213104.5667-2-list@eworm.de
Signed-off-by: David Sommerseth <davids@openvpn.net>