Add support for installing PostgreSQL database server

[dbeech]

I suggest we use a well-established role from Ansible Galaxy to do this, instead of re-inventing the wheel. https://github.com/geerlingguy/ansible-role-postgresql

[lhoss]

@dbeech I could not agree more :) and the best, I already choose exactly that role myself to install postgres, and have working playbooks for both CDH and HDP clusters:

• CDH deployments : https://github.com/scigility/hadoop-ops/blob/master/ansible/install-cdh-postgres-dbs.yml
• HDP deployments: https://github.com/scigility/hadoop-ops/blob/master/ansible/install-hdp-postgres-dbs.yml

Furthermore I deployed postgresql from different yum repositories, to get a newer version than the default centos7 (v9.2.x):

• RH SCL: https://github.com/scigility/hadoop-ops/blob/master/ansible/install-postgres-scl-rh.yml
  • requires: https://github.com/geerlingguy/ansible-role-postgresql/pull/96
• PGDG: https://github.com/scigility/hadoop-ops/blob/master/ansible/install-postgres-pgdg-EL.yml