GRILL-617: Support loading hadoop jars from CDH4 style distro

First one is for cdh4, where hadoop-core is present at $HADOOP_HOME/client-0.20/hadoop-core-2.0.0-mr1-cdh4.3.0.jar, while for cdh3 it is present at $HADOOP_HOME/hadoop-core-0.20.2-cdh3u5.jar