Anbangx/fix aggregator

Hi,

Some small changes in this branch:

1. add a script to automatically generate times and size from log
2. change to use only one nc and only one dev in pregel test suite. Make test easy.
3. fix aggregator - Don't use preReadAggregator anymore. But like Jake mentioned before, the aggregator in pregel is only allowed in single iteration. If we want to use cross iteration, it will be very expensive. Thank you Jake for this PR #76 . Hope it can solve this problem.