Comment 14 for bug 1754174

I don't understand why this bug is happening. Context:
- when run from the live session by clicking on the icon, ubiquity runs under sudo and runs entirely as root. this succeeds.
- when run from the "Install Ubuntu" option in the splash screen, ubiquity starts as root with PKEXEC_UID set in the environment telling it the uid to drop privileges to; and drops privileges to run as non-root most of the time.
- there is code in ubiquity which is supposed to raise privileges back to root before calling any operations that require root.
- the "Install Ubuntu" option works from both Ubuntu 18.04 beta2 and from Lubuntu 17.10.1. Only in Lubuntu 18.04 beta2 is it broken.
- several of the commands which are failing in the logs on Lubuntu due to permissions are operations that can only be run via 'chroot' which is a privileged operation - so the chroot succeeds, and then afterwards the commands lack permissions to operate on the target filesystem?!
- none of the changes to the ubiquity codebase since 17.10 seem to be relevant.
- the code around the point at which the install fails - basically when trying to run the first installer plugin (the language plugin) via scripts/plugininstall.py - doesn't include any privilege-handling code. So there seems to be an assumption that this code is running as root already. Clearly this assumption proves invalid, but I'm unclear where this is supposed to be happening.