Avoid doing this on non-Docker-for-{Mac,Win} editions (which don't run vsudd)
by checking for vsudd.pid and avoid doing it on Docker-for-Win (for now) by
checking for /sys/bus/vmbus (as /etc/init.d/vsudd does too).
Ideally we would just check for /var/run/syslog.vsock but this may not have
arrived yet (typically vsudd is now started immediately prior to syslog and it
forks via start-stop-daemon and thus before it creates the socket). Since
syslogd will reopen as needed we don't want to delay boot either here or in the
vsudd initscript to await the arrival of the socket.
Signed-off-by: Ian Campbell <ian.campbell@docker.com>
