Merge "Fix the flaky test MaxServerPrune_Binder" am: b3a2bf0940

    ASSERT_TRUE(mDnsClient.SetResolversWithTls(servers, domains, kDefaultParams, "", fingerprints));

    // If the private DNS validation hasn't completed yet before backend DNS servers stop,

    // TLS servers will get stuck in handleOneRequest(), which causes this test stuck in

    // ~DnsTlsFrontend() because the TLS server loop threads can't be terminated.

    // So, wait for private DNS validation done before stopping backend DNS servers.

    for (int i = 0; i < MAXNS; i++) {

        ALOGI("Waiting for private DNS validation on %s.", tls[i]->listen_address().c_str());

        EXPECT_TRUE(tls[i]->waitForQueries(1, 5000));

        ALOGI("private DNS validation on %s done.", tls[i]->listen_address().c_str());

    }

    std::vector<std::string> res_servers;

    std::vector<std::string> res_domains;

    std::vector<std::string> res_tls_servers;