Add script to package tests + workload runner in a standalone tarball

This adds a new make_test_tarball.sh script which will copy all the required
dependencies to run the workload runner and impala Python tests outside of the
Impala source tree. The goal is to make it very easy to run workloads
on an arbitrary cluster without having to clone the impala source tree or build anything.
As part of the make process, it will generate a simple set-env.sh script that
configures the required environment variables, such as IMPALA_HOME and PYTHONPATH.

It does not include any test data files, but contains the scripts required to recreate
the table metadata. This tarball + a snapshot file should be sufficient to run most of
the tests.

Change-Id: If3bb12defa3c16a368a353075f8e784442464746
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3605
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>
Tested-by: jenkins
(cherry picked from commit 4ff721236fb9e8bb6254d6ba46205a0ed147bf20)
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3654