uninstall-devices fails early

[edbaunton]

Currently if your chroot gets into a bad state where not all the devices were cleanly uninstalled, you cannot easily fix it. The --uninstall-devices is
not best effort and bails after failing the first one.

For example, /dev/shm can be busy so when it is attempted to be unlinked it fails. This then leaves all the other devices installed.

Expected behavior
--uninstall-devices does not give up as soon as the first uninstall fails. Rather it should warn and then ultimately return non-zero.

[juergbi]

The /dev/shm issue should be solved by #14. However, I agree, --uninstall-devices should still not fail early.