Add a hand-coded __init__.py into jw.pkg.cmds.distro. Auto-generation
works fine, but has to run before it can work. For a freshly
downloaded toplevel Makefile / project-dirs-minimal.mk, the targets
pkg-install-xxx-deps requires a working package manager without
jw-pkg built.
Signed-off-by: Jan Lindemann <jan@janware.com>