_hard_reboot func changes device bus addresses

[wuhao]

We found this problem in Juno. But I think that may be reproduced in each version.

Currently, _hard_reboot will regenerate instance config file, which changes device bus addresses when the instance has hot plug-in devices, like attach interfaces or volumes. If the address changes, then windows will treat it as a new device.Unfortunately, power_on operation and reboot operations in some cases will call the _hard_reboot function, which is not what we expected.

Reproduce steps:
* create a window instance.
* create a new nic.
* shut down the instance and then power on it.

Windows will find a new nic device.