revise the logging format

I really like the way that airflow formats their log files

e.g.

```
[2016-01-05 15:38:52,840] {models.py:985} INFO - Executing <Task(BashOperator): make_kwd> on 2016-01-01 16:30:34.333773
[2016-01-05 15:38:53,575] {models.py:1088} ERROR - Bash command failed
```
