Update repo source from wrouesnel to prometheus-community

[wrossmann]

Per PR #16 the wrouesnel repo was absorbed into prometheus community some time ago. Please merge that change.

For those the wish to make it work in the meantime just set the following variables:

postgres_exporter_url: "https://github.com/prometheus-community/postgres_exporter/releases/download/v{{ postgres_exporter_version }}/{{ postgres_exporter_dist }}.tar.gz"
postgres_exporter_dist: postgres_exporter-{{ postgres_exporter_version }}.linux-amd64

Additionally, to use a more recent version than 0.8.0 [current default in this role] you will likely need to change to a different DSN format:

postgres_exporter_datasource: "postgresql://postgres@:5432/postgres?host=/var/run/postgresql/&sslmode=disable"

And, just for the sake of convenience, you can use the below to use the most recent exporter version as of this writing:

postgres_exporter_version: "0.11.1"
postgres_exporter_checksum: "sha256:ec27e2a52b764c4313076ea6db335607cc40fb8a503dcb74d9517dc8baf049f0"

Though you'll likely also need to override the queries.yml that ships with this role, as it is also outdated. You can get it from:

https://github.com/prometheus-community/postgres_exporter/blob/v0.11.1/queries.yaml