Changed group sysadmins from gid 999 to 900 to avoid conflict in RHEL7 with built in group polkitd:999

Added new mephisto (future possible cheaha) users stuartm and sam9412 - https://trac.uabgrid.uab.edu/atlab/ticket/820

Added liamvdp user to new galaxy related groups in cheaha_users.pp: https://trac.uabgrid.uab.edu/atlab/ticket/816#comment:4

Added new cheaha user eric.bylaska-pnnl from Pacific Northwest National Labratory collaborating with Ryoichi Kawai - https://trac.uabgrid.uab.edu/atlab/ticket/802

The groups conflict was not addressed the the last commit, moving all jpr groups into the systadmins.pp class

Last commit had a conflict with groups for user jpr 'Error: Could not retrieve catalog from remote server: Error 400 on SERVER: Parameter 'groups' is already set on User[jpr] by #<Puppet::Resource::Type:0x7f20a8832078> at /etc/puppet/environments/production/modules/users/manifests/cheaha_users.pp:80; cannot redefine at 17:/etc/puppet/environments/production/modules/users/manifests/sysadmins.pp on node nas-02.uabgrid.uab.edu