Port scheduler hints extension to v3 API Part 2

Ports the scheduler hints extensions and the corresponding
unittests to the v3 framework. Moves the commented out tests from
the v3 version of test_servers to the config drive extension
unittests.

Partially implements blueprint nova-v3-api

Change-Id: If0164e3e80927662ec3b955df4642f03b2d18853
Merge "Port scheduler hints extension to v3 API Part 2"