code: protected List<DockerCloud> getAvailableDockerClouds(Label label) {
          return getAllDockerClouds().stream()
                  .filter(cloud ->
                          cloud.canProvision(label) &&
                                  (countCurrentDockerSlaves(cloud) >= 0) &&
                                  (countCurrentDockerSlaves(cloud) < cloud.getContainerCap()))
                  .collect(Collectors.toList());
      }
docs: Get a list of available DockerCloud clouds which are not at max
  capacity.
  
  @param label A label expression of a Job Run requiring an executor.
  @return A list of available DockerCloud clouds.