MINOR: Also accept SIGHUP/SIGTERM in systemd-wrapper

MINOR: Also accept SIGHUP/SIGTERM in systemd-wrapper

My proposal is to let haproxy-systemd-wrapper also accept normal
SIGHUP/SIGTERM signals to play nicely with other process managers
besides just systemd. In my use case, this will be for using with
runit which has to ability to change the signal used for a
"reload" or "stop" command. It also might be worth renaming this
bin to just haproxy-wrapper or something of that sort to separate
itself away from systemd. But that's a different discussion. :)