Original purpose of this patch is that replacing deprecated
webob.Accept.best_match method to acceptable_offers to analize
'Accept' header of a HTTP request.
Instead of fixing legacy wsgi code, refactor v2 wsgi code not to
use legacy wsgi code because legacy wsgi code is complicated
and v2 wsgi code uses legacy wsgi code very little.
Original purpose mentioned above is included in the refactoring
at the same time. This patch includes the followng changes
related to wsgi framework too.
* check of Content-Type header is also enhanced.
* check of Version header for api_versions API is relaxed.
Change-Id: I4ca0beda850ecd14d65d7bc1a59d465c5ecfeacb
00d8f69f09