Pace requires `make build`

[jdahm]

If a user runs make savepoint_tests_* from within Pace, Docker returns Unable to find image 'us.gcr.io/vcm-ml/pace:latest' locally. We need to run make build first. This artifact doesn't even exist on https://console.cloud.google.com/gcr/images/vcm-ml?referrer=search&project=vcm-ml.