Change v3 shelve to v2.1

This patch changes v3 shelve API to v2.1 and makes v2
unit tests share between v2 and v2.1.
The differences between v2 and v3 are described on the wiki page
https://wiki.openstack.org/wiki/NovaAPIv2tov3 .

Partially implements blueprint v2-on-v3-api
Change-Id: Ie4cd72d23592fe2bd1a66137b12bb84400ccfc18
Merge "Change v3 shelve to v2.1"