When SIGUSR1 is received, haproxy enters in soft-stop and quits when no
connection remains.
It can happen that the instance remains alive for a long time, depending
on timeouts and traffic. This option ensures that soft-stop won't run
for too long.
Example:
global
hard-stop-after 30s # Once in soft-stop, the instance will remain
# alive for at most 30 seconds.