test: rmwprog: support command-line argument

test: rmwprog: support command-line argument

This test can easily be extended to allow more than 2 atomic increments
per thread. For instance, it's interesting to see the model-checker
behavior for 4 increments per thread. Now, you can do this with a simple
numeric command-line argument that gets passed to the user program.

Example - run rmwprog with 4 increments per thread, viewing the
execution traces verbosely:

  ./run.sh test/rmwprog.o -v -- 4