Massively parallel directory creation fail

[cfrontin]

When running in a massively parallel way on HPC, for instance, this line can fail. It appears that there's a race condition that can get multiple processors past the L320 if statement before this line is reached, then the "if directory exists" condition changes after evaluating the if statement on L320.

Adding a keyword argument for exists_ok=True into the os.makedirs call on L320 can be used to allow this condition to be ok, I think.