give a (small and random) value of smpi/ois and smpi/os flags for mpich3 tests. Ratio...

give a (small and random) value of smpi/ois and smpi/os flags for mpich3 tests. Rationale is that it can speedup some tests a lot, as without it and async_small_thres, a lot a small messages can be sent at the same time in a loop, piling in the system and causing a lot of lag when lmm needs to handle all of these messages at once