Fix schema of list hypervisors API

Nova "list hypervisors" API returns like the following response which
includes "status" and "state",

{
  "hypervisors": [
    {
      "status": "enabled",
      "state": "up",
      "id": 1,
      "hypervisor_hostname": "devstack-trusty-948085"
    }
  ]
}

but its schema doesn't contain them.
So this patch adds them into the schema.

Change-Id: Ibfd905b8df10e5ff737f0f00a96de989a24c98aa
diff --git a/tempest/api_schema/response/compute/hypervisors.py b/tempest/api_schema/response/compute/hypervisors.py
index e9e1bc9..273b579 100644
--- a/tempest/api_schema/response/compute/hypervisors.py
+++ b/tempest/api_schema/response/compute/hypervisors.py
@@ -160,9 +160,14 @@
                 'items': {
                     'type': 'object',
                     'properties': {
+                        'status': {'type': 'string'},
+                        'state': {'type': 'string'},
                         'id': {'type': ['integer', 'string']},
                         'hypervisor_hostname': {'type': 'string'}
                     },
+                    # NOTE: When loading os-hypervisor-status extension,
+                    # a response contains status and state. So these params
+                    # should not be required.
                     'required': ['id', 'hypervisor_hostname']
                 }
             }