HoS itests shouldn't depend on a Spark distribution

The HoS integration tests download a full Spark Distribution (a tar-ball) from CloudFront. It uses this distribution to run Spark locally. It runs a few tests with Spark in embedded mode, and some tests against a local Spark on YARN cluster. The itests/pom.xml actually contains scripts to download the tar-ball from a pre-defined location.

This is problematic because the Spark Distribution shades all its dependencies, including Hadoop dependencies. This can cause problems when upgrading the Hadoop version for Hive (ref: HIVE-13930).

Removing it will also avoid having to download the tar-ball during every build, and simplify the build process for the itests module.

The Hive itests should instead directly depend on Spark artifacts published in Maven Central. It will require some effort to get this working. The current Hive Spark Client uses a launch script in the Spark installation to run Spark jobs. The script basically does some setup work and invokes org.apache.spark.deploy.SparkSubmit. It is possible to invoke this class directly, which avoids the need to have a full Spark distribution available locally (in fact this option already exists, but isn't tested).

There may be other issues around classpath conflicts between Hive and Spark. For example, Hive and Spark require different versions of Kyro. One solution to this would be to take Spark artifacts and shade Kyro inside them.