Backport some v3 scheduler hints API UT to v2 API

This patch adds below v3 scheduler hints API unittest
into V2 API to improve V2 API unittesting.

Change-Id: I5352906567c1c90c33d0709addaeb445fe1a7371
Convert v3 server SchedulerHints plugin to v2.1

This patch converts v3 server SchedulerHints plugin 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.

Note- to make V2.1 SchedulerHints extension work in V3 framework,
an extra parameter (request body) is being passed in server_create
function of each extensions.

Partially implements blueprint v2-on-v3-api

Change-Id: I8a0d50efcda6fcd12971a41505127de5987eec18
Merge "Backport some v3 scheduler hints API UT to v2 API"
Merge "Convert v3 server SchedulerHints plugin to v2.1"