Add support for custom PostgreSQL host-based authentication

This changeset adds support for custom PostgreSQL host-based
authentication via Ansible variables. `postgresql_hba_mapping` is a list
of maps that contain the following attributes:

- type
- database
- user
- address
- method

Inside a playbook, PostgreSQL HBA could be customized using:

postgresql_hba_mapping:
  - { type: "host", database: "all", user: " address: "0.0.0.0/0",
      method: "md5" }
0.2.0
Merge branch 'release/0.2.0' into develop