Test 1 -- MPI Ping-pong ring

In this test the ranks on each host perform ping-pong with the ranks on their neighbor-host. The order of operations is

- first loop with 1 rank per host participating
  - the 1 rank on host1 and host2 do ping-pong
  - the 1 rank on host2 and host3 do ping-pong
  - the 1 rank on host3 and host4 do ping-pong
  - ...
- next loop with 2 ranks per host participating
  - the 2 ranks on host1 and host2 do ping-pong
  - the 2 ranks on host2 and host3 do ping-pong
  - the 2 ranks on host3 and host4 do ping-pong
  - ...
- next loop with 3 ranks per host participating
- ...

The textual output of the test shows all the above lines, but the graph only shows lines for the number of ranks used per host being 1/8, 1/4, 1/2, 3/4, and 1 (all) of the ranks per host since it gets too cluttered otherwise.