BUG/MEDIUM: mworker: stop every tasks in the master

The master is not supposed to run (at the moment) any task before the
polling loop, the created tasks should be run only in the workers but in
the master they should be disabled or removed.

No backport needed.
diff --git a/src/haproxy.c b/src/haproxy.c
index f8fba14..6c96794 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -895,6 +895,7 @@
 
 	mworker_unblock_signals();
 	mworker_cleanlisteners();
+	mworker_cleantasks();
 
 	mworker_catch_sigchld(NULL); /* ensure we clean the children in case
 				     some SIGCHLD were lost */