Add gsutil tool builder to the release and cache it on worker image creation
Add gsutil tool builder to the release and cache it on worker image creation

Also add rudimentary smoke tests to cloudbuild.yaml for bazel, gcloud and
gsutil

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MOE_MIGRATED_REVID=129475673
APPROVED=

google-octo/cloud-builders,GoogleCloudPlatform/cloud-builders,GoogleCloudPlatform/cloud-builders,GoogleCloudPlatform/cloud-builders,google-octo/cloud-builders,google-octo/cloud-builders,GoogleCloudPlatform/cloud-builders,GoogleCloudPlatform/cloud-builders,google-octo/cloud-builders,google-octo/cloud-builders,GoogleCloudPlatform/cloud-builders,google-octo/cloud-builders,google-octo/cloud-builders,GoogleCloudPlatform/cloud-builders