This commit reworks the `org.osbuild.container-deploy` stage to
not use a tmp storage when mounting the container image. This
is needed because of [0] but it should generally be fine because
inside the stages the real /var is a tmpfs (which is why we
triggered the bug in the first place).
[0] https://github.com/containers/storage/issues/1779
Extract a new helper `make_fake_tree()` that generalizes the existing
helper `make_fake_input_tree()`. The later will always create the
content under `{basedir}/tree` which is convinient for input tree
based tests but too specialized when using it in different contexts.
The existing `make_fake_input_tree()` is preserved unchanged and
becomes just a tiny wrapper.
This is a convenient way for tests to assert that some nested dicts
(like a parsed json) has a particular key/value somewhere in it.
For example:
assert_dict_has(config, "toplevel.subitem.key", True)
This commit adds `osbuild.testutil.imports.import_module_from_path`
that can be used to import arbitrary python source files. This
allows importing files from the stages directory that have a
non python friendly filename like `org.osbuild.kickstart`.
