MAHOUT-1616 Hadoop client

I changed the hadoop related dependencies in the project root and mrlegacy to hadoop-client.

Now to build mahout against to hadoop 1.2.1, run `mvn clean package`
For another version of hadoop, try `mvn clean package -Dhadoop.version=YOUR_HADOOP_VERSION`

Tests pass, but I currently don't have access to an actual cluster. Could somebody please test this on a cluster and report the results?

This would allow us to automatically support multiple hadoop versions, including vendors', and would result in simpler poms. 
If it works, I will change mahout-spark module accordingly.