code: func (containers Containers) stripProvisioningDuplicates() (deduplicated Containers) {
  	seenProvisioningKeys := make(map[string]bool)
  	for _, container := range containers {
  		// for 2 containers that would the same provisioning
  		// commands, the key should be equal
  		key := container.BuildParams().Context() + "#" + container.Image()
  		if _, ok := seenProvisioningKeys[key]; !ok {
  			deduplicated = append(deduplicated, container)
  			seenProvisioningKeys[key] = true
  		}
  	}
  	return
  }
docs: // returns another list of containers, stripping out containers which
  // would trigger some commands more than once for provisioning.