Mounts should always be cleaned up

I tried pmbootsrap yesterday and on multiple occasions it errored or I stopped it with Ctrl-c.

I then tried to delete $HOME/.local/var/pmbootstrap/ but I was getting some errors. Since I have had similar problems with chroots, I checked the output of mount and lo and behold, there were a ton of entries that all led to pmbootstrap.

I think this also indirectly led to pmbootsrap install --android-recovery-zip trying to create an infinitely large zip, but I haven't debugged the cause of that because I had quite enough problems getting the machine working with an HDD it couldn't write to.

Conclusion: pmbootstrap should clean up properly when it exits, be it normally or abnormally. I think what could work is wrapping the whole thing in a shell script that runs ./pmbootstrap.py and when that exits it runs the cleanup.