Move test_size, bind_fid and wait_for_completion to common code.

Move wait_for_completion to common code and change simple/pingpong.c to
work with wait_for_completion.
I see. I think in this check in I'll set the option of the smaller sizes to "2" (except 1<<1, 1<<3 and 1<<5 that is used in the ud_pingpong test) to make them shadow contents, and for ud_pingpong I'll check for max_msg_size. We can come up with a more sophisticated size_option solution in a later time, does that sound a plan?