Use make's --output-sync option when running tests inside VMs,
so that if we're building with parallelization the output doesn't
get scrambled.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-Id: <20180803085230.30574-6-peter.maydell@linaro.org>
Signed-off-by: NFam Zheng <famz@redhat.com>