CI: various improvements
Make it possible to run all CI scripts via pmbootstrap ci
and other CI related fixes.
- CI: shellcheck: make pmbootstrap ci compatible
- CI: shellcheck: ignore SC3043 (instead of ignoring it inline every time)
- CI: let install_pmbootstrap.sh do pmb init
- CI: upgrade-compat: make pmbootstrap ci compatible
- CI: upgrade-compat: set default UI=none
- CI: upgrade-compat: fix 2x chroot still active msg
See commit messages for details.