old_contents: import os
  c.IPClusterEngines.engine_launcher_class = 'MPI'
  if 'NPROC' in os.environ:
      c.IPClusterEngines.n = int(os.environ['NPROC'])
  
new_contents: import os
  c.IPClusterEngines.engine_launcher_class = 'MPI'
  if 'JPY_ENGINES' in os.environ:
      c.IPClusterEngines.n = int(os.environ['JPY_ENGINES'])
  
subject: Rename env variable for # MPI processes