Convert v3 hypervisor plugin to v2.1

This patch convert v3 hypervisor plugin to v2.1 and makes v2
unit tests share between v2 and v2.1.

Unit tests has been modified in optimized way.

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: I23ffc10d4c0170cb43ef8aeebf69ae2794a08827
Merge "Convert v3 hypervisor plugin to v2.1"