Fix restapi bugs
Fix restapi bugs

* urljoin splits on /, but the results often had empty strings which
  was causing problems. This nixes the empty strings
* RestAPIException didn't originally take kwargs--now it does. That
  makes it easier to pass additional data through the exception on
  what the Response looked like

CarlFK/steve,CarlFK/steve,willkg/steve,willkg/steve,pyvideo/steve,CarlFK/steve,willkg/steve,pyvideo/steve,pyvideo/steve