def host_power_action(self, action):
        if action in ("reboot", "shutdown"):
            return self._host.host_power_action(action)
        else:
            msg = _("Host startup on XenServer is not supported.")
            raise NotImplementedError(msg)
The only valid values for 'action' on XenServer are 'reboot' or
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/virt/xenapi/driver.py/XenAPIDriver.host_power_action