reset received_configuration_ for every request sent

[mikaelarguedas]

fixes #81

[JVSelvag]

I found this problem when running my own tests for my software project on my test server. They failed there, never on my local computer. Then I did the same fix that you have done now, but I still got failing tests sometimes on the test server. (I've begun to wonder if the configurationCallback() is actually fired twice in rapid succession when setting the configuration; one time with the current (old) configuration and then one more time with the new one). Anyway, I've fixed the problem in my code by adding a short delay (100 ms) between setting and getting configuration. That seems to do it, the tests work now.
Your code looks good. You may merge, but I'm not sure if the problem is completely fixed.

[mikaelarguedas]

thanks for the feedback, I did test it both locally and on the farm that tend to have slower machines and I haven't seen any failure so far. I'll add a delay, as you suggested, in the test if the error you saw on your server shows up on our server farm. Thanks!