Refactor RaidNode to remove dependence on map reduce

I am refactoring the RaidNode code as follows: The base class RaidNode will contain the common functionality needed for raiding files. The derived class LocalRaidNode contains an implementation of RaidNode that performs raiding locally. The derived class DistRaidNode performs raiding using map reduce jobs. This way, only DistRaidNode has a dependency on map reduce code and RaidNode and LocalRaidNode can be moved to HDFS.