This commit makes state filename unique for a given pipeline (and
remove this state in the cleaning phase), and adds a unique tag to the
runners created for the pipeline for jobs not to be run in runners
from other pipelines that run in parallel.

Fix #1: Update documentation after terraform MR 1 changes

Closes #1

See merge request !2

terraform project now use destruct provisioner to unregister gitlab
runner too.
terraform!1