MINOR: mworker: use ha_notice to announce a new worker

 Displays the PID and the relative PID when we fork a new worker with
 ha_notice().
diff --git a/src/haproxy.c b/src/haproxy.c
index 7835621..6a1397a 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -3003,7 +3003,7 @@
 				if (global.mode & MODE_MWORKER) {
 					struct mworker_proc *child;
 
-					qfprintf(stdout, "New worker #%d (%d) forked\n", relative_pid, ret);
+					ha_notice("New worker #%d (%d) forked\n", relative_pid, ret);
 					/* find the right mworker_proc */
 					list_for_each_entry(child, &proc_list, list) {
 						if (child->relative_pid == relative_pid &&