[SPARK-1459] Use local path (and not complete URL) when opening local lo...

...g file.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #375 from vanzin/event-file and squashes the following commits:

f673029 [Marcelo Vanzin] [SPARK-1459] Use local path (and not complete URL) when opening local log file.
SPARK-1496: Have jarOfClass return Option[String]

A simple change, mostly had to change a bunch of example code.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #438 from pwendell/jar-of-class and squashes the following commits:

aa010ff [Patrick Wendell] SPARK-1496: Have jarOfClass return Option[String]