rosconsole format for rospy

quick & dirty solution for issue:
https://github.com/ros/ros_comm/issues/517

Since in python it uses [logging module](https://docs.python.org/2/library/logging.html) and in C++ it uses [log4cxx](http://logging.apache.org/log4cxx/index.html), I could not find 1 to 1 translation for some outputs. For example, `${thread}` and `${logger}` does not match well with that of C++.

Also I was not sure if this file was a good place to write this functionality. @dirk-thomas recommended to check out [this file](https://github.com/ros/ros_comm/blob/fab4840ef79f5334bcd043e057a1909183842159/clients/rospy/src/rospy/core.py#L119) but this file was easier to make change. Let me know if you have suggestions,
What if I wrap the code using rospy with try & catch block? Similar to the [line 145-151 of this file](https://github.com/ros/ros_comm/blob/indigo-devel/tools/rosgraph/src/rosgraph/roslogging.py#L145-L151)? Is there some special problem with using `get_name` function of rospy? I tried to modify [core.py](https://github.com/ros/ros_comm/blob/indigo-devel/clients/rospy/src/rospy/core.py) file, for example somehow try to overwrite this `emit` function from `core.py`.. would that be right direction? any other suggestions?