'Get extra Specs key-value of the mentioned flavor and key.
For a full list of available parameters, please refer to the official
API reference:
https://developer.openstack.org/api-ref/compute/#show-an-extra-spec-for-a-flavor'

def show_flavor_extra_spec(self, flavor_id, key):

    (resp, body) = self.get(('flavors/%s/os-extra_specs/%s' % (flavor_id, key)))
    body = json.loads(body)
    self.validate_response(schema_extra_specs.set_get_flavor_extra_specs_key, resp, body)
    return rest_client.ResponseBody(resp, body)
