Change v3 quota-sets API to v2.1

This patch changes v3 quota-sets 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: I96377c2c5c02e00cb70eadde225f3e17d0e0025c
Merge "Change v3 quota-sets API to v2.1"