The [published docs for 1.5.0](http://spark.apache.org/docs/1.5.0/api/java/org/apache/spark/streaming/) have a bunch of test classes in them.  The only way I can reproduce this is to `test:compile` before running `unidoc`.  To prevent this from happening again, I've added a clean before doc generation.

Author: Michael Armbrust <michael@databricks.com>

Closes #8787 from marmbrus/testsInDocs.