Add a cloudbuild.yaml to push images to GCR when changes are merged.
Add a cloudbuild.yaml to push images to GCR when changes are merged.

Fixes https://github.com/GoogleCloudPlatform/distroless/issues/19

GoogleContainerTools/distroless,istio/distroless,istio/distroless,GoogleContainerTools/distroless,mattmoor/distroless,mattmoor/distroless,GoogleContainerTools/distroless,istio/distroless,mattmoor/distroless