Message format: Expand field-width for event-counter to 6

While looking at the log of one of the jobs latest large-scale MT tests submitted by @elmsheus, I noticed log lines like:

03:53:38 MuonInsideOutRecoAlg....MuonTrackSummaryHelperTool1...   1 WARNING Number of hits in road < 0 in first projection: -2, setting = 0. (nhits in first projection = -2)

eg the event-count abbreviated to '1...' for numbers > 9999. This MR expands the field with to 6, so this should not happen any more.