backup.lock shouldn't exist on persistant storage

## User Story

It turns out my cron scheduled backups haven't been running due to a stale lock file. I recommend changing the default location of the backup.lock file to tmpfs so it won't survive a reboot.

## Basic info

* **Distro:** [Ubuntu 20.04]
* **Game:** [Minecraft]
* **Command:** [backup]
* **LinuxGSM version:** [v20.3.3]

## Further Information

* Instead of `./lgsm/lock/` probably `/run/lock/`
* Alternatively , you could store the pid of the backup command in the lock file and check that it still exists.

## To Reproduce

Steps to reproduce the behaviour:
* have a stale backup.lock from 2 months ago.
* cron the backup command nightly
* enjoy no backups when you need it (I know, my fault for not checking).

## Expected behaviour
* A reboot should clear the lock, as the backup process would also not survive a reboot.