Mpich yarn hydra

Hi, this is a pull request from Steven, who is doing internship jobs at Chen Wenguang's laboratory in Tsinghua University. This mpich-yarn-hydra branch hilights on reusing hadoop's daemon sshd, using a ssh-supported process manager Hydra, support on the newest version of MPICH, and making it easier for starters to use. It has passed NAS Parallel Benchmark NPB-MPI-IS-32-A, NPB-MPI-IS-32-B, NPB-MPI-IS-32-C.