BUG/MINOR: checks: free memory allocated for tasklets

The check->wait_list.task and agent->wait_list.task were not
freed properly on deinit().

This patch should be backported to 1.9.
diff --git a/src/haproxy.c b/src/haproxy.c
index 93ce987..603f084 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2295,6 +2295,11 @@
 			if (s->agent.task)
 				task_destroy(s->agent.task);
 
+			if (s->check.wait_list.task)
+				tasklet_free(s->check.wait_list.task);
+			if (s->agent.wait_list.task)
+				tasklet_free(s->agent.wait_list.task);
+
 			if (s->warmup)
 				task_destroy(s->warmup);