Making only process 0 check if the Catalyst script exists.

Process 0 now is the only process that checks whether a Catalyst
Python script exists and then broadcasts that info to other
processes. This is one less way we'll kill the file system
when running at scale.

Change-Id: I50fc220666d236c6d6f5f49eb89654168ac3e3d0
Merge topic '14784_PythonCatalyst_better_IO' into next

737ca051 Making only process 0 check if the Catalyst script exists.