Added use_sudo as a kwarg to the sudo function.

This PR is to add a kwarg to reboot to allow ```run``` instead of just ```sudo``` within the reboot function.

No test written as no test currently exists for reboot.

Output from pylint is:
```
pylint2 -E operations.py 
No config file found, using default configuration
************* Module fabric.operations
E:827,54: Instance of 'list' has no 'endswith' member (but some types could not be inferred) (maybe-no-member)
E:828,53: Instance of 'list' has no 'endswith' member (but some types could not be inferred) (maybe-no-member)
```
Which isn't related to my change (though after looking at the code I can see why pylint is confused).