- Bump version: 9.15.1 → 9.15.2

- Fix zypper add lock operations

This commit fixes the arguments passed to zypper in add lock
operations.

- Add correct GPL-3.0-or-later license

Add the correct license reference in the spec License field

Fixes #732

- Make container compression a configuration option

Change the ContainerBuilder class to evaluate on the
configuration options to decide if the container archive
should be compressed or not. By default the archive will
be compressed, thus there is no change to the former behavior
but can be setup in ~/.config/kiwi/config.yml as follows:

container:
- compress: none|xz