Attempted to clean up issues in pom.xml.

This reveals #524. I was playing around with the AvroParquetRDD and ran into a few issues; specifically, the Apache Commons HTTP library that we were depending on _in ADAM_ is in conflict with the version that the AWS SDK needs. Removing this conflict causes the compile to fail. I also found that we weren't running the `S3Test` tagged unit tests at all, which is fun.

Also, as an aside, why was the AWS SDK library marked as `provided`? Am I missing something (i.e., is there a way to side step the dependency conflict above), or...?

CC @tdanford @carlyeks