Changes to lock file behavior

## User Story

As a server admin, I want backup to give the choice of wiping an previous failed backup so that failed backups do no hang around.

## Basic info

* Distro \[Ubuntu 18.04]
* Game \[Garry's Mod]
* Feature: backup

## Further Information

Game Server backup command EG: ./wurmserver backup

if LGSM finds the backup lock file. from a previous failed attempt, the whole process just fails.
No description given of where to find the lock file.

Would it be possible that if the lock file is found to present the user with a choice to delete it and start a new backup?