tests/docker: add a debian-native image and make available

tests/docker: add a debian-native image and make available

This image is intended for building whatever the native versions of
QEMU are for the host architecture. This will hopefully be an aid for
3rd parties who want to be able to build QEMU themselves without
redoing all the dependencies themselves.

We disable the registry because we currently don't have multi-arch
support there.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210922151528.2192966-1-alex.bennee@linaro.org>