Quiet stderr output, particularly for multi-simulations

Quiet stderr output, particularly for multi-simulations

* removed printing of DD info to stderr
* printed multi-simulation information only once in places where
  repetition is clearly redundant (Some repetition remains,
  but only from each simulation master.)
* add option to not print result of multi-simulation check
  if it passed, so that we don't have to print things to
  stderr/stdout just because the .log file is not yet open
* printing of diagnostics about the number of MPI
  processes present when mdrun starts only goes (once) to
  each debug file, and not to stderr
* reduced printing of diagnostics about the number of OpenMP
  threads; now goes to stderr only on SIMMASTER, or
  once to each debug file
* clarified errors and informational messages about selecting
  the number of OpenMP threads

Fixes #1078, refs #1083

Change-Id: If782259bcd62ddd9be325393930080b70c5cfb4e