We inadvertently broke the ability to run local builds when the code
was re-factored. The result was the run stanza failing to find the
docker image with it's qemu/ prefix.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Fixes: d39eaa22 ("tests/docker: simplify docker-TEST@IMAGE targets")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220613171258.1905715-5-alex.bennee@linaro.org>