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,
Please reduce the redundant code part and only do the minimal stuff inside the try block:

    try:
        from rospy import get_name
        node_name = get_name()
    except ImportError:
        node_name = '<unknown_node_name>'
    msg = msg.replace('${node}', node_name)