tests: NGINX_TEST_CHECK_LEAK detects memoryleak because nginx can not free resolver ctx quickly.

This was introduce in commit acd5364 which is use to resovle double free of resolver ctx.
This issue happens only when nginx can not get any reply from the dns server until timeout.

Author: zhuizhuhaomeng

t/127-uthread-kill.t

@@ -139,6 +139,7 @@ lua clean up the timer for pending ngx.sleep
 === TEST 3: kill pending resolver
 --- config
     resolver 127.0.0.2:12345;
+    resolver_timeout 5ms;
     location /lua {
         content_by_lua '
             local function f()