BUG/MEDIUM: mworker: remain in mworker mode during reload

BUG/MEDIUM: mworker: remain in mworker mode during reload

If you reload an haproxy started in master-worker mode with
"master-worker" in the configuration, and no "-W" argument,
the new process lost the fact that is was in master-worker mode
resulting in weird behaviors.

The bigest problem is that if it is reloaded with an bad configuration,
the master will exits instead of remaining in waitpid mode.

This problem was discovered in bug #443.

Should be backported in every version using the master-worker mode.
(as far as 1.8)