Add shelve_offload test for Nova API

On compute nodes which are configured with shelved_offload_time = -1,
the shelve API changes a server status to SHELVED and a server image
remains in the node. The shelve_offload API offloads the server image
from the node. This patch adds the API test for Nova API.

Partially implements blueprint nova-v3-api-tests

Change-Id: Iaa2f94c3381c8b68df7fe132e1c13b4b81962b8c
5 files changed