Fix Spark build.

Our build requires the CDH distribution of hadoop.  This was working for us data dudes because we had the necessary jars in our local maven repo as an artifact of setting up data-hadoop.

I've added the Cloudera Maven repo to the list of repositories to check when building Spark.

This fixes the build issue @snormore and @charlescng are hitting.

Reviewers: @airhorns @bouk @tyro89