tests: Replace ncat with socat in migration test and drop ncat from containers

nmap / ncat has a somewhat problematic license (e.g. saying claiming that derived work is also considered for software that "is designed specifically to execute Covered Software and parse the results", e.g. by executing ncat from your own program, you might already fall into this category) - so for example in openSUSE 16, you can only find it in the "non-OSS" repository. We are currently only using it in the migration functional test, and that likely does not fall into this "derived work" category yet (since it is also doing some other stuff), but still, to be safe, we should move away from using it now. Unfortunately, switching to one of the other flavors of netcat is also not a real option (see commit f700abbbeb6ab68a3446d1fb168a934d), but socat should be a solid replacement here instead. To avoid that someone else easily uses ncat again, let's also remove it from our container files now. Suggested-by: Daniel P. Berrangé <berrange@redhat.com> Signed-off-by: Thomas Huth <thuth@redhat.com> Acked-by: Peter Xu <peterx@redhat.com> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Message-ID: <20260316183016.239526-1-thuth@redhat.com> Message-ID: <20260320155107.2143191-9-alex.bennee@linaro.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>