SPARK-1565 (Addendum): Replace `run-example` with `spark-submit`.

Gives a nicely formatted message to the user when `run-example` is run to
tell them to use `spark-submit`.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #704 from pwendell/examples and squashes the following commits:

1996ee8 [Patrick Wendell] Feedback form Andrew
3eb7803 [Patrick Wendell] Suggestions from TD
2474668 [Patrick Wendell] SPARK-1565 (Addendum): Replace `run-example` with `spark-submit`.