Exclude jopt from kafka dependency.

Kafka uses an older version of jopt that causes bad conflicts with the version
used by spark-perf. It's not easy to remove this downstream because of the way
that spark-perf uses Spark (by including a spark assembly as an unmanaged jar).
This fixes the problem at its source by just never including it.
Merge pull request #110 from pwendell/master

Exclude jopt from kafka dependency.

Kafka uses an older version of jopt that causes bad conflicts with the version
used by spark-perf. It's not easy to remove this downstream because of the way
that spark-perf uses Spark (by including a spark assembly as an unmanaged jar).
This fixes the problem at its source by just never including it.