Improve application of terraform specs and propagation of output to the pipeline

[orange-cloudfoundry]

Improve application of terraform specs and propagation of output to the pipeline

[o-orand]

In fact, only terraform-provider-cloudfoundry is downloaded each time, we use terraform docker official image, so coucourse cache is usually used.
Currently, the proposed terraform-resource must have a S3 back-end to persist terraform state file, we are using git. So some works is required to propose a Git back-end support or move to S3-like out tfstate

[gberche-orange]

As a transient alternative to moving to a terraform concourse resource, fetching the terraform cloudfoundry provider into the docker image might simplify things, as contributed by @ArthurHlt into https://hub.docker.com/r/orangeopensource/concourse/tags/ and whose source is into https://github.com/orange-cloudfoundry/concourse-containers/blob/master/terraform/Dockerfile#L3-L5

[o-orand]

Before using concourse-containers, a tag mechanism should be implemented. Otherwise we won't be able to decide terraform upgrade (ie upgrades are going to occur on each new publication)

[gberche-orange]

Cross referencing orange-cloudfoundry/concourse-containers#1 orange-cloudfoundry/concourse-containers#2 and