Add CI pipeline

Add CI pipelines

Initial checks

• terraform-validate checks the terraform compiles
• ansible-lint runs a linter across the ansible playbooks

Main pipeline

• Creates nodes with terrafrom
• Runs ansible to configure nodes
• Runs gitlab-qa against the configured stack (PH)
• Tears down the nodes with terraform

Terraform state is backed in a bucket identified by STATE_GCS_BUCKET.

Credentials to a project need to be supplied in GCLOUD_CREDENTIALS_JSON

All variables used should be described in /qa/README.md

Closes gitlab-org/omnibus-gitlab#3395 (closed)