Login Node Implementation for slurm

[DeepikaKrishnaiah]

Issues Resolved by this Pull Request

Fixes #444

Description of the Solution

1. A separate node created for login node
2. Login node has the same configuration as a compute node with slurmd.service running
3. New role start_workers_service added - This role takes care of updating copies of updated slurm.conf to all the compute nodes and login node.
4. serial: 1 added in start_worker role. Without this slurm.conf was updating incorrectly since ansible executes in parallel on multiple remote nodes. Now slurm.conf is updated uniquely on each compute node and login node and the same copy is placed in all nodes of the cluster(manager, compute and login node) with login node info.

Suggested Reviewers

@lwilson @j0hnL