Add clean up of previous images

[danieldean]

This is a contribution for #273. Let me know if there are any issues!

All tests passed apart from doc building. It works when running for me and cleans up as expected.

[netbrain]

Great stuff, we really need some housekeeping.

However need to robustify the script a bit, and i think there's some mix of indentation usage (spaces). See comments.

[netbrain]

Another thing, the dont_clean option should also be present in flake.nix

[glennvl]

@danieldean The zwift.sh script was moved to a src directory in #272, so you need to rebase your branch before these changes can be merged (git rebase master).

[danieldean]

@danieldean The zwift.sh script was moved to a src directory in #272, so you need to rebase your branch before these changes can be merged (git rebase master).

Thanks and noted. At the moment I think the array splitting is a blocker so will resolve that first if possible then rebase.

[danieldean]

Ok... hopefully all issues resolved and all good now with the rebase. Bash is deceptively complicated!

[netbrain]

After this, i think it looks ok,

[danieldean]

Ok, further suggested changes applied. Hope all is good now? I know some more Bash that I did to start with...

[netbrain]

Merging as is, it's fine.