Change ViewBuilder into v2.1 for servers

This patch changes v3 servers' ViewBuilder to v2.1. And also
change related unittests and api sample tests.

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: Ie68d46daa91ef43c84eeef479c0986d5e7f15719
Merge "Change ViewBuilder into v2.1 for servers"