Force TimedRotatingFileHandler to rollover at startup.

Due to a bug in python 2.6 and 2.7.0,
TimedRotatingFileHandler does not rotate log file at startup.
Force a doRollover() call at startup to mitigate the problem.

Python-Id: http://bugs.python.org/issue8117
Change-Id: I801af3e8ac3771c3b1b44fca813626a066e95df8