'Set a bootable flag for a volume - true or false.
For a full list of available parameters, please refer to the official
API reference:
http://developer.openstack.org/api-ref/block-storage/v2/#update-volume-bootable-status'

def set_bootable_volume(self, volume_id, **kwargs):

    post_body = json.dumps({'os-set_bootable': kwargs})
    url = ('volumes/%s/action' % volume_id)
    (resp, body) = self.post(url, post_body)
    self.expected_success(200, resp.status)
    return rest_client.ResponseBody(resp, body)
