Check if bf.barrier() is working properly

[hanbinhu]

Currently bf.barrier() doesn't make sure the order of the outputs is correct, for example the following code snippets

for i in range(2):
  bf.barrier()
  if rank == 0:
    print("A")
  bf.barrier()
  print("B")

Expected Output of bfrun -np 2

A
B
B
A
B
B

Possible output now:

A
B
B
B
A
B