MEDIUM: systemd: Type=forking in unit file

Adding Type=forking in the unit file ensure better monitoring from
systemd. During a systemctl start the tool is able to return an error if
it didn't work with this option.
diff --git a/contrib/systemd/haproxy.service.in b/contrib/systemd/haproxy.service.in
index 05bb716..ca38d70 100644
--- a/contrib/systemd/haproxy.service.in
+++ b/contrib/systemd/haproxy.service.in
@@ -12,6 +12,7 @@
 ExecReload=/bin/kill -USR2 $MAINPID
 KillMode=mixed
 Restart=always
+Type=forking
 
 [Install]
 WantedBy=multi-user.target