Changes V3 server_actions extension into v2.1

This patch changes v3 server_actions API to v2.1, and also share v2.1 and v2
test case.
rename server_actions back to instance_actions.
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: I8f11dc5f199711e1c98badfbe0035883d9c15573
Merge "Changes V3 server_actions extension into v2.1"