The registry url is <project>/<repo>/qemu/<image>

Perhaps we should rationalise that some day but for now.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200724064509.331-2-alex.bennee@linaro.org>