t_client.sh: Make OpenVPN write PID file to avoid various sudo issues

t_client.sh: Make OpenVPN write PID file to avoid various sudo issues

This resolves an issue where $! returns the PID of the sudo process instead
of the PID of OpenVPN and when sudo does not properly propagate signales
down to OpenVPN.

Trac: #738
Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1474104026-20615-1-git-send-email-davids@openvpn.net>
URL: http://www.mail-archive.com/search?l=mid&q=1474104026-20615-1-git-send-email-davids@openvpn.net
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit e0926ebfe55347843af701216be9598827a1367a)