Added destroy command to base Terraform template

lib/gitlab/ci/templates/Terraform.latest.gitlab-ci.yml

@@ -6,6 +6,7 @@ stages:
   - validate
   - build
   - deploy
+  - cleanup
 
 init:
   extends: .init

lib/gitlab/ci/templates/Terraform/Base.latest.gitlab-ci.yml

@@ -51,3 +51,9 @@ cache:
   when: manual
   only:
     - master
+
+.destroy: &destroy
+  stage: cleanup
+  script:
+    - gitlab-terraform destroy
+  when: manual