varnishlog exists when sending SIGHUP

The currently shipped systemd unit file causes varnishlog to exit when SIGHUP is sent to it.

SIGHUP has two meanings for varnishlog:
 1) when running in daemon mode: reopen logfile
 2) when not running in daemon mode: exit

Since the current systemd unit file doesn't run varnishlog in daemon mode, a reload will result in a stop, instead of a reopen of the logfile.

This systemd unit file does work properly (for me, at least):

[Unit]
Description=Varnish HTTP accelerator log daemon
After=varnish.service

[Service]
RuntimeDirectory=varnishlog
Type=forking
User=varnishlog
Group=varnish
ExecStart=/usr/bin/varnishlog -D -a -w /var/log/varnish/varnish.log -P /run/varnishlog/varnishlog.pid
ExecReload=/bin/kill -HUP $MAINPID
PIDFile=/run/varnishlog/varnishlog.pid

[Install]
WantedBy=multi-user.target