Introduces collective overhead with the sends/receives and other

The changes made in model-net-mpi-replay.c includes:

1. Introducing collective overhead with the sends/receives.
2. Adding different background traffic pattern: all-to-all, 2D stencil, and nearest neighbor. The reverse handler might need to be fixed for optimistic mode.
3. Modifying output of collective stats for collective validation study, the reverse handler is on to-do list.