scripts/arch-run: don't use deprecated server/nowait options

The very fact that QEMU drops the deprecation warning while running is
enough to confuse the its-migration test into failing. The boolean
options server and wait have accepted the long form options for a long
time.

Tested-by: Zenghui Yu <yuzenghui@huawei.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Shashi Mallela <shashi.mallela@linaro.org>
Signed-off-by: Andrew Jones <drjones@redhat.com>