MO: Flush after dumping the arguments to stdout (#570)

MO: Flush after dumping the arguments to stdout (#570)

When stdout is not a terminal, Python will buffer it by default. This
means that a consumer of MO's output will not see the argument information
until the buffer is flushed, which will normally only happen once MO
finishes (which might take a while).

Flushing stdout explicitly allows the consumer to see this info as soon
as it's printed.