Re #8306. Only show a run number if one is available.

Previously, you would see "Run #0 ended" in some situations, when the
actual run number was different.
Re #8306. Reduce log level from warning to debug.

These messages appear sometimes, but are really not useful to the user.
They don't appear to signal a significant or externally noticeable problem.
Merge remote-tracking branch 'origin/bugfix/8306_misleading_log_message'