This improves formatting for HTTP errors. keystoneauth's HttpErrors
are now caught an re-formatted to include the body of the http response.
Work items:
* Introduce the "http_error_formatter" function decorator, which catches
an re-formats keystoneauths HttpErrors.
* Introduce the "format_http_errors" class decorator, which applies the
"http_error_formatter" to all functions of a class.
* Add an "HttpDecoratorMeta" to the "BaseManager" class. This will decorate
all functions of classes inheriting from "BaseManager" with the
"http_error_formatter" decorator.
Change-Id: I6735f1fa8d876a87e2b7d4aaa533d5a32b085735
d28c5bc4dd