Cinder Pagination Sorting Enhancements

Currently, the sorting support for Cinder allows the caller to specify a
single sort key and sort direction. This blueprint enhances the sorting
support for the /volumes and /volumes/detail APIs so that multiple sort keys
and sort directions can be supplied on the request.

bp cinder-pagination
APIImpact

Change-Id: Ia8781ed2d37fa2a0cb711a7f98d06919fc8a79d0
Merge "Cinder Pagination Sorting Enhancements"