debug-shell: don't be picky, use /bin/sh rather than /bin/bash

In a minimal initramfs, one might not always have the full bash available.
Typically if using busybox.
Revert "nspawn: catch config mistake of specifying -b and args"

This reverts commit cb96a2c69a312fb089fef4501650f4fc40a1420b.

It is not a mistake to pass args when -b is specified. They will simply
be passed on to the container's init.

The manpage needs fixing, that's true.
kernel-install: add kernel-install tool
kernel-install(8): add documentation about the configuration files used
nspawn: add --bind= and --bind-ro= to bind mount host paths into the container
kernel-install: remove LANG=
tests: add a few more tests to test-util.c

Add asserts on the resutls in FOREACH_WORD_QUOTED
Added tests for:
  FOREACH_WORD
  strstrip
  delete_chars
  in_charset
kernel-install: fixed paths in boot loader entry

For the loader entry a relative path has to be used.
kernel-install: replace URLs with man pages in the error messages
kernel-install: create the loader entries with absolute paths relative to /boot
kernel-install: rename the loader entry filename

The wildcard matching the default loader entry should always be able to point to
the same machine.

So instead of sorting by <distribution>-<kernel-version>-<machine-id>
we better sort by <machine-id>-<kernel-version>.
TODO: update
query for user unit information in the journal

Add --user-unit= to make it possible to query for user logs by the name
of the service.