Allow setting different root dir for apt

[egvimo]

See #171

Implemented as command line argument instead of env var.

Additionally I've refactored a little bit. Fixed linting issues and created a separate function to use in other scripts.

[macetw]

Definitely needed to manage within a docker container. Suggest moving this forward.

[macetw]

This PR is only managing it for the apt script. Do we need this setting for any of the other scripts in this code?

A quick glance found deleted_libraries.py would require this change. fstab_check.sh. Gosh all of them?

[egvimo]

I've created an exporter using the script from this PR which runs inside a Kubernetes cluster inside a container exporting the metrics via ServiceMonitor: https://github.com/egvimo/apt-exporter
This works even with a read only mount of the host directory.

[anarcat]

should this be merged, or should we look at removing apt_info.py in favor of the apt-exporter?

[dswarbrick]

should this be merged, or should we look at removing apt_info.py in favor of the apt-exporter?

If we remove a script simply because a dedicated exporter exists, then we would also need to remove the smartmon.{py,sh} and ipmitool scripts.

[anarcat]

If we remove a script simply because a dedicated exporter exists, then we would also need to remove the smartmon.{py,sh} and ipmitool scripts.

that would solve #119 at least :p