Add current time stamp at logging

 If is hard to track log when multiple nodes are deployed and ipop is running
for a long time. For debug purpose, current time stamp is added at the head of
each log line. New logging.cc file is copied and slightly modified from
talk/base/logging.cc and replace original logging.cc file.

 I'm not sure whether there is simpler or neat way to do this. Let me know if you have better idea.