tests/docker: add a linux-user testing focused image
We happily use all the cross images for both cross-building QEMU as
well as building the linux-user tests. However calling docker from
within docker seems not to work. As we can build in Debian anyway why
not include an image that has all the compilers available for
non-docker invocation.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <
20200701135652.1366-33-alex.bennee@linaro.org>