This change is mainly to support Terraform Cloud and other use cases
which don't support a `terraform init -reconfigure`.

This is achieved with a new optional `TF_INIT_NO_RECONFIGURE` environment
variable which can be set to `true` which prevents a `-reconfigure` to
be added to the `terraform init` command.

This change is backwards-compatible.

Closes: https://gitlab.com/gitlab-org/terraform-images/-/issues/65
Closes: https://gitlab.com/gitlab-org/terraform-images/-/issues/79
Closes: https://gitlab.com/gitlab-org/terraform-images/-/issues/14