Convert v3 ExtendedAvailabilityZone api to v2.1

This patch changes v3 ExtendedAvailabilityZone 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: I49baff38b7a9dabd40550267c2119fe84137594f
Merge "Convert v3 ExtendedAvailabilityZone api to v2.1"