Add support for negative tests with admin client

This adds the missing support for admin clients and implements an
example based on flavor creation. Instead of listing all result code
checks it is now possible to define on default.

Change-Id: I9512c1b91eb227e35faf24e3e88ed73a6ed3b734
Partially-implements: bp autogen-negative-tests
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
Merge "Add support for negative tests with admin client"
Merge "Add shelve_offload test for Nova API"