Add support for installing from default debian repositories for ARM targets

This PR adds support for 
  - installing from default debian repositories, rather than the postgresql repos
  - backward compatibility down to 9.1

Postgresql repositories do NOT have binaries for ARM architectures.
I need to use the packages supplied by debian themselves for this. The debian repos have only 9.1 installed.

As Ansible handle mutliple booleans forms (True/yes/…) you should remove the `== True` part.