Changes V3 remote_console extension into v2.1

This patch changes v3 remote_console 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: I5f15ec39d7201b2da3d7afbf1d0774e64e68c8fe
Merge "Changes V3 remote_console extension into v2.1"