Merge pull request #147 from JoshRosen/fix-java-api-completeness-checker

Add spark-tools assembly to spark-class'ss classpath

This commit adds an assembly for `spark-tools` and adds it to `spark-class`'s classpath, allowing the JavaAPICompletenessChecker to be run against Spark 0.8+ with

    ./spark-class org.apache.spark.tools.JavaAPICompletenessChecker

Previously, this tool was run through the `run` script.  I chose to add this to `run-example` because I didn't want to duplicate code in a `run-tool` script.

(cherry picked from commit 3efc0195625977335914f0a18cf32bd4e9b1d6d4)
Signed-off-by: Reynold Xin <rxin@apache.org>