show puppet timestamps in verbose mode

here's a quick example how to add timestamps piping stdout through a small script: http://blog.jasonantman.com/2011/09/quick-and-simple-timestamping-of-debug-logs/

with this, a puppetrun would look like this:

elijah, could you implement this please ? It would be super useful for debugging race conditions like #5269 (closed).

not sure if we should enable it always or only in verbose mode.

(from redmine: created on 2014-04-04, closed on 2014-04-08, relates #7795)