Add install process of gcc-gfortran because of the dependency about MLlib
Add gcc_fortran role and delete installation of gcc-gfortran from cdh5_spark role.
This is because gcc-gfortran should be installed to all nodes not only to client node.
Additionally, I modified a playbook to install CDH5's Spark Core.
Delete unnecessary procedure about installation of gcc-gfortran
Merge branch 'master' of https://github.com/dobachi/ansible-cdh5 into dev/readme