Merge branch 'collectd' into 'master'

add a collectd role that can be deploed to compute and login nodes

See merge request !128

roles/collectd/tasks/main.yml

+---
+- name: install collectd
+  yum: name=collectd state=installed
+  become: true
+  become_user: root
+
+- name: install collectd config
+  template: src=collectd.conf.j2 dest=/etc/collectd.d/collectd.conf mode=0600 owner=root group=root
+  become: true
+  become_user: root
+
+- name: start collectd service
+  service: name=collectd state=started enabled=true
+  become: true
+  become_user: root
+