Exception handler improvement.

This commit addresses an issue where sometimes Rackspace sends down the
error dict directrly, rather than with "message" and "detail" nested
within another key.

This will make the error be processed correctly in either case. It also
adds the details to the error string on the output, when available.
Pagination support

This commit adds support for listing records beyond the first 100, by
detecting and following Rackspace pagination markers.