Clean up initial log output

Clean up initial log output

The rank count was incorrect when thread-MPI has not yet spawned
threads. It could only be fixed if we would have made that choice
before we open the log file, but we want to be able to report problems
to the log file from hardware detection or tpr reading which occur
before rank choice.

Host name, rank count and rank ID are all reported later, alongside
other such information, so there is no need to duplicate and
complicate our code.

PID is now reported later alongside other similar information. The log
file output looks reasonable, aligned, etc.

Noted TODO for future clean up.

Fixes #2775

Change-Id: Ifda6c44bfe28628934f4614e20eeeef436d80707