Add new error for invalid response

There are a number of places where we expect a certain format of
response. If it's not found we often end up raising a KeyError when
accessing data.

Create a new Exception type that is raised when a HTTP response is not
appropriate for parsing and use it within authentication calls.

Closes-Bug: #1307306
Change-Id: I3cf2db07a8e76ee17702130e9efb0edf640d293a
Merge "Add new error for invalid response"