Respect the -D flag
Respect the -D flag

It looks like edfbffb85f4684b87a906c6c1f1aeba6aaf870aa caused the
OVPN_DNS variable to start being ignored, meaning the -D flag was a
no-op.

myplacedk/docker-openvpn,elie195/docker-openvpn,slamont/docker-openvpn,hjnijlunsing/docker-openvpn-armhf,richnologies/docker-openvpn,kylemanna/docker-openvpn,rdev02/docker-openvpn