PARQUET-89: Add hadoop-2 test profile for Travis CI.

This also fixes problems that prevented hadoop-2 from passing:
* Dynamically resolve counter methods in parquet-hadoop
* Parameterize pig version with hadoop-2 support
* Update pig test for hadoop-2 change (no nulls allowed)
* Update parquet-hive to depend on hadoop-client

The travis config will now run each test profile in a different run.
Fixed