tests: test-resolve: wait until all queries are completed

This is a follow-up for 4a134c49

Fixes:

$ ./test-resolve
209.132.183.105:80
209.132.183.105:80
canonical name: n/a
193.99.144.85:0
[2a02:2e0:3fe:1001:7777:772e:2:85]:0
canonical name: www.heise.de
Host: web.heise.de -- Serv: http

$ ./test-resolve
193.99.144.85:0
[2a02:2e0:3fe:1001:7777:772e:2:85]:0
canonical name: www.heise.de
Host: web.heise.de -- Serv: http

$ ./test-resolve
...