feature: updating hdfs_consumer-related things for greater flexibility

Addresses need for hwx hadoop to ship with a kafka -> hdfs writer.

1) minor refactor of run_contrib_app.rb to better find an hdfs host

2) added logic to install_common.rb to allow option not to install
   custom hadoop-core jar

3) modified hdfs_consumer.properties.erb to accommodate the
   run_contrib_app.rb refactor

Squashed commit of the following:

commit 1a95edc63541234c9f58e121d753d8eaca3b3f6c
Author: eric katerman <eric@infochimps.com>
Date:   Tue Mar 18 00:09:17 2014 -0700

    updating hdfs_consumer-related things for greater flexibility

    Change-Id: I0b5c8796e942e16a468424f9ab35702db700363e

Change-Id: Ia9adab8d26d1c5acc76e7bb68fa5594d0faf45f3