QnAMakerService correctly builds hostname URL & throws error w/o URL

[Zerryth]

Fixes #939

Description

• Issue 1: URL built for hostname would always append "/qnamaker" to QnAMakerService.hostname, even when the hostname already had /qnamaker in the hostname string

  • QnAMakerService will now only append /qnamaker to hostname, if it does not end in /qnamaker already
  • Ex 1: https://myservice.azurewebsites.net => https://myservice.azurewebsites.net/qnamaker
  • Ex 2: https://MyServiceThatDoesntNeedAppending.azurewebsites.net/qnamaker remains the same

• Issue 2: previously if QnAMakerService's first parameter receives a source that does not have a hostname, in the URL class's logic, it would throw invalid URL error when constructing URL + base to create QnAMakerService.hostname

  • As per Steven's advice, QnAMakerService now throws an error, clearly stating that the hostname is required in the source to construct the QnAMakerService properly
  • this is because nothing actually can be done w/regards to QnAMaker unless you have a hostname

[cleemullins]

If I'm being picky, "/qnamaker" isn't a host name.

"/qnamaker" is a path segment.

In this case, I think the underlying IQnAService is messed up, so we can't change it.