If hadoop_tar_url variable is defined, an installation will be performed using a tar file downloaded from {{hadoop_tar_url}} instead of using the deb files defined in `deburl` or `rpmurl`.
Fix typo
update `nfsexport` module: add option `state` to ensure the filesystem is mounted _and_ exported
Add support for SLURM on CentOS 6 (Needs to download and compile slurm)
Remove `blacs-openmpi` package which is not available on CentOS 6 (apparently)
cosmetic changes