Overview of changes
- Add deprecation notices to the POSIX shell implementation
- Add test for the new --distro option
- Drop the FGC namespace from the fedora-toolbox images
- Fix miscellaneous issues pointed out by https://www.shellcheck.net/
- Handle hosts with /etc/localtime as absolute symlink
- Improve README.md
- Improve the Zuul configuration
- Mount /mnt only if it is available
- Refactor the system tests, and use bats-assert and bats-support
- Test that sudo doesn't require a password
- Update the manuals