run.py: start QEMU in nographic mode

This is in order to make it send Ctrl+C to the guest instead
of killing the VM. Leads to less surprises when working with
interactive shell inside OSv.

To suppress the new behavior run with --g or --with-graphic.

Relates to issue #49.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>