CONFIG: accept -decompose-dict=xyz for Run functions and mpirunDebug

- interpret as '-decomposeParDict xyz' for simpler scripting:
  A empty value ("") as well as "none" or "false" values are ignored.

  Eg,
      unset decompDict
      if some_condition; then decompDict=decomposeParDict-12; fi

      runParallel -decompose-dict=$decompDict ...

ENH: more generous when scanning decomposeParDict for numberOfSubdomains

- assume file is in system/ directory if not otherwise found