setup posgres within the common role

Postgres is used by several roles, but the setup is currently part of the 'mailserver' role. By moving it to 'common', it's possible to disable the mailserver without breaking the others.

roles/common/tasks/main.yml

 - include: security.yml tags=security
 - include: ntp.yml tags=ntp
 - include: google_auth.yml tags=google_auth
+- include: postgres.yml

roles/common/tasks/postgres.yml

+---
+# Defines tasks applicable for postgreSQL
+
+- name: Install Postgres
+  apt: pkg={{ item }} state=installed
+  with_items:
+    - postgresql
+    - python-psycopg2
+  tags:
+    - dependencies
+
+- name: Set password for PostgreSQL admin user
+  become: true
+  become_user: postgres
+  postgresql_user: name={{ db_admin_username }} password={{ db_admin_password }} encrypted=yes

roles/mailserver/tasks/postfix.yml

-- name: Install Postgres
-  apt: pkg=postgresql state=present
-  tags:
-    - dependencies
-
 - name: Install Postfix and related packages
   apt: pkg={{ item }} state=installed
   with_items:
   tags:
     - dependencies
 
-- name: Set password for PostgreSQL admin user
-  become: true
-  become_user: postgres
-  postgresql_user: name={{ db_admin_username }} password={{ db_admin_password }} encrypted=yes
-  notify: import sql postfix
-
 - name: Create database user for mail server
   postgresql_user: login_host=localhost login_user={{ db_admin_username }} login_password="{{ db_admin_password }}" name={{ mail_db_username }} password="{{ mail_db_password }}" encrypted=yes state=present
   notify: import sql postfix