BUG/MEDIUM: mworker: fix the reload with an -- option

BUG/MEDIUM: mworker: fix the reload with an -- option

When HAProxy is started with a '--' option, all following parameters are
considered configuration files. You can't add new options after a '--'.

The current reload system of the master-worker adds extra options at the
end of the arguments list. Which is a problem if HAProxy was started wih
'--'.

This patch fixes the issue by copying the new option at the beginning of
the arguments list instead of the end.

This patch must be backported as far as 1.8.