Issue #34 Deal with changed counter sub group names in hadoop2
Updating the hadoop version to enum, javadocs and adding more unit tests
Adding in a HadoopVersion class instead of having the enum inside Constants
Updating to use HadoopVersion class instead of a nested enum  inside Constants
Merge pull request #37 from vrushalic/return_counter_subgroup

Issue #34 Deal with changed counter sub group names in hadoop2