Addressed suggestions from pull request. Added aSync, as well as onload function to XMLHttpRequest. Looks like it works, although I still have a feeling something is off. I've tested the httprequest  using a manual request via a browser plugin when the Radical server is down, and the browser test results in the expected Status of 0 (server doesn't exist). however, the testServerConnection either returns a resolved promise (beliving a 200 response status), OR because I'm misunderstanding the goal of the test-carddav-connector's test function. Should it return a successfully passed test even if a promise is brought back as rejected?