Use Terraform to allocate IP and DNS for Review applications

As see in #59 (closed) , the cause of the pipeline failures was 99% of the time due not to a failure of the helm command, but rather the attempt to shared a single regional static IP for all LoadBalancers deployed with these charts. To get around this problem, I've added in a snippet of Terraform (ci/terraform) that allocates a single IP address and the two DNS entries (gitlab-*, registry-*) to point to this newly created IP address.

Basically: https://gitlab.com/charts/helm.gitlab.io/issues/59#note_49646542 helm-terraform-ip-dns

• Added a Dockerfile (closing #35 (closed)) that contains the needed tools, and is based on alpine
• Added terraform_* functions to .gitlab-ci.yml to init/up/down the Terraform resource
• Added several secret variables to CI

Closes #59 (closed) Closes #35 (closed)

cc @omame @pcarranza