Comment out nb_test, since it's not entirely correct.
This was meant to test out the case when MPI_Test is not nonblocking. However, we ended up assuming that MPI_Win_lock will be nonblocking. That is not specified by the standard and might not be true. Commenting this out till be find a better way to test the original problem with MPI_Test. Fixes #1910. Signed-off-by: Rajeev Thakur <email@example.com>