combine pam_slurm and pam_sshd so we have only one slightly less confusing role

Former-commit-id: 976f3bc1

roles/pam_slurm/tasks/main.yml

----
-- name: "Copy access.conf"
-  template: src=access.conf.j2 dest=/etc/security/access.conf
-  become: true
-  become_user: root
-
-- name: "Copy password sshd pam config"
-  template: src=sshd.j2 dest=/etc/pam.d/sshd
-  become: true
-  become_user: root
-

roles/pam_sshd/README.md

+Install an sshd PAM config definition
+
+we leverage pam_access to ensure that the ec2-user and members of the systems group and always login
+
+we use nologin on the login nodes during maintaince to retrict user login
+
+we use pam_slurm_adopt on the compute nodes so that only users with running jobs can login a given node.
+
+default is to configure as a login node. Use the variable computenodepam to config as a compute node (i.e. enable pam_slurm_adopt)

roles/pam_sshd/tasks/main.yml

+---
+- name: "Copy access.conf"
+  template: src=access.conf.j2 dest=/etc/security/access.conf
+  become: true
+  become_user: root
+
 - name: "Copy password sshd pam config"
-  template: src=sshd.j2 dest=/etc/pam.d/sshd
+  template: src=loginnodes_sshd.j2 dest=/etc/pam.d/sshd
   become: true
   become_user: root
+  when: comptenodepam is undefined
 
+- name: "Copy password sshd pam config"
+  template: src=computenodes_sshd.j2 dest=/etc/pam.d/sshd
+  become: true
+  become_user: root
+  when: comptenodepam is undefined