Automatic merge from submit-queue
GCI: Add two GCI specific metadata pairs
This PR adds two GCI specific metadata pairs when using GCI image.
(1) "gci-update-strategy": by default the GCI in-place updater is enabled. It means that when a new image is released, the instance on the old image will be upgraded to the new image. In this change, we turn it off;
(2) "gci-ensure-gke-docker": GCI is built with two versions of docker. When this metadata is set to "true", the version satisfying kubernetes qualification will be used. Setting this metadata prevents from using incorrect docker version.
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