Another round to remove final modifier to private methods because it is not needed

Remove final modifier to private methods because it is not needed.
Those methods are final by default.

Author: Henry Saputra <henry.saputra@gmail.com>

Closes #168 from hsaputra/remove_final_privatemethods_1 and squashes the following commits:

860b512 [Henry Saputra] Remove final modifier to private methods because it is not needed. It is final by default.
[FLINK-1139] Added FinalizeOnMaster hook to run code after the last task of an OutputFormat completed
[FLINK-1139] Fixed HadoopOutputFormat to run with DOP > 1