Create private-runners-manager-X in GCP

As part of #3531 (closed) we should prepare two new machines in GCP to prepare a copy of private-runners-manager-X

• create machines:
  • private-runners-manager-3
    • create /etc/ipaddress.txt with external IP address
  • private-runners-manager-4
    • create /etc/ipaddress.txt with external IP address
• assign DNS records:
  • private-runners-manager-3.gitlab.com IN A 35.207.32.187
  • private-runners-manager-4.gitlab.com IN A 35.207.13.227
• prepare Runner tokens (gitlab-runner register ...)
  • private-runners-manager-3.gitlab.com
    • for GitLab.com (specific!)
    • for dev.gitlab.org
  • private-runners-manager-4.gitlab.com
    • for GitLab.com (specific!)
    • for dev.gitlab.org
• prepare new roles in chef:
  • gitlab-runner-prm-gce as child of gitlab-runner-prm
  • gitlab-runner-prm-gce-us-east1-c as child of gitlab-runner-prm-gce
  • gitlab-runner-prm-gce-us-east1-d as child of gitlab-runner-prm-gce
  • gitlab-runner-prm3 as child of gitlab-runner-prm-gce-us-east1-d
    • create secrets for gitlab-runner-prm3 based on gitlab-runner-srm3
    • add Runner token to secrets
  • gitlab-runner-prm4 as child of gitlab-runner-prm-gce-us-east1-d
    • create secrets for gitlab-runner-prm4 based on gitlab-runner-srm4
    • add Runner token to secrets
• bootstrap chef nodes:
  • private-runners-manager-3.gitlab.com, based on gitlab-runner-prm3 role
  • private-runners-manager-4.gitlab.com, based on gitlab-runner-prm4 role
• add new nodes to Prometheus (prometheus-server role):
  • in node job (public_hosts)
  • in private-runners job (target)
• update graph at https://gitlab.com/gitlab-com/runbooks/blob/master/howto/update-gitlab-runner-on-managers.md (runbooks!600)