When the -seed option is given, call qemu_guest_random_seed_main,
putting the subsystem into deterministic mode.  Pass derived seeds
to each cpu created; which is a no-op unless the subsystem is in
deterministic mode.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>