Power-cycle a Component to Handle Bus Errors

Bus errors are caused by machine-check exceptions. If a bus error occurs, try power-cycling the component.

Power down the components. The physIDlist is a comma-separated list of components present on the system.
```
crayadm@smw> xtcli power down physIDlist
```
Power up the components.
```
crayadm@smw> xtcli power up physIDlist
```