tests: wait for put before performing get

tests/dhtrunnertester.cpp

@@ -50,7 +50,11 @@ DhtRunnerTester::testGetPut() {
     auto key = dht::InfoHash::get("123");
     dht::Value val {"hey"};
     auto val_data = val.data;
-    node1.put(key, std::move(val));
+    std::promise<bool> p;
+    node1.put(key, std::move(val), [&](bool ok){
+        p.set_value(ok);
+    });
+    CPPUNIT_ASSERT(p.get_future().get());
     auto vals = node2.get(key).get();
     CPPUNIT_ASSERT(not vals.empty());
     CPPUNIT_ASSERT(vals.front()->data == val_data);