Add os-migration tests for Nova v3 API

v3 os-migration API returns a body which includes the info like:

 {
   "migrations": [
     {
       "id": 1,
       "status": "finished",
       "instance_uuid": "4ed20c05-6bcb-46c5-a6a4-115523660283",
       "source_node": "source-host",
       "source_compute": "source-host",
       "dest_node": "dest-host",
       "dest_compute": "dest-host",
       "dest_host": "10.21.43.148",
       "old_instance_type_id": 6,
       "new_instance_type_id": 7
       "created_at": "2014-02-17T18:59:18.000000",
       "updated_at": "2014-02-17T18:59:31.000000"
     }
   ]
 }

This patch adds this API tests.

Partially implements blueprint nova-v3-api-tests

Change-Id: I2bc8efa6eb5034ec2c4516fd147b8221600cf571
Verify the response attributes of 'startup_host' API

This patch verifies the response attributes of 'startup_host' API.
The response body format of v2:
{
    "host": "57f5de2fa5b44f14974a4f50b9ffcbf8",
    "power_action": "startup"
}

The response body format of v3:
{
    "host": {
        "host": "4b392b27930343bbaa27fd5d8328a564",
        "power_action": "startup"
    }
}

Partially implements blueprint nova-api-attribute-test
Change-Id: If73daa85c374ce2ae8187cdc7f4929c8647ebe66
Merge "Add os-migration tests for Nova v3 API"
Merge "Verify the response attributes of 'startup_host' API"