Wait for topic creation to complete in tests

[noslowerdna]

When we create topics in our tests, we need to wait for the creation to complete, since it's async with the result wrapping a collection of futures.

For reference solution see example code from open-source Kafka,

        Admin adminClient = Admin.create(adminProps);
        NewTopic newTopic = new NewTopic(topic, DEFAULT_NUM_PARTITIONS, DEFAULT_REPLICATION_FACTOR);
        try {
            adminClient.createTopics(Collections.singleton(newTopic)).all().get();
        } catch (ExecutionException | InterruptedException e) {
            System.out.printf("Creation of topic %s failed%n", topic);
            throw new RuntimeException(e);
        } finally {
            Utils.closeQuietly(adminClient, "AdminClient");
        }