Add gcp nested libvirt openshift installer

[sallyom]

Adding job to openshift-installer against a 4.0 libvirt install. This has been requested because developers depend on the libvirt workflow with openshift/installer. Keeping this job optional for now until we know it's reliable.
Depends on openshift/installer#625

@stevekuznetsov for this job, we'll need:

• the quay pull-secret from cluster-secrets-aws copied into the cluster-secrets-gcp secret. done
• 2 images necessary for the install in openshift-gce-devel-ci project, from this repo: https://github.com/sallyom/openshift4-libvirt-gcp/tree/ci-openshift4-libvirt-gcp and with packer build openshift4-libvirt-source.json and packer build openshift4-libvirt.json

this needs to merge first #2143

[stevekuznetsov]

/lgtm

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sallyom, stevekuznetsov

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[openshift-ci-robot]

@sallyom: Updated the following 2 configmaps:

• ci-operator-configs configmap using the following files:
  • key openshift-installer-master.yaml using file ci-operator/config/openshift/installer/openshift-installer-master.yaml
• job-config configmap using the following files:
  • key openshift-installer-master-presubmits.yaml using file ci-operator/jobs/openshift/installer/openshift-installer-master-presubmits.yaml

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In response to this:

Adding job to openshift-installer against a 4.0 libvirt install. This has been requested because developers depend on the libvirt workflow with openshift/installer. Keeping this job optional for now until we know it's reliable.
Depends on openshift/installer#625

@stevekuznetsov for this job, we'll need:

• the quay pull-secret from cluster-secrets-aws copied into the cluster-secrets-gcp secret. done
• 2 images necessary for the install in openshift-gce-devel-ci project, from this repo: https://github.com/sallyom/openshift4-libvirt-gcp/tree/ci-openshift4-libvirt-gcp and with packer build openshift4-libvirt-source.json and packer build openshift4-libvirt.json

this needs to merge first #2143

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