Change v3 admin_actions to v2.1

This patch changes v3 admin_actions API to v2.1 and make v2
unit tests share between v2 and v2.1, move v3 testcase to 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: I6fa4a8bd45d0f32f2a61bc6d8ff7e0fbb5fa7f26
Merge "Change v3 admin_actions to v2.1"