code: public Set<Machine> list(String cliPathExec, String field, String value) {
          final Set<Machine> machines = new HashSet<>();
          List<String> output =
              commandLineExecutor.execCommandAsArray(createDockerMachineCommand(cliPathExec), "ls", "--filter",
                  field + "=" + value);
          output = findHeader(output);
  
          if (!output.isEmpty()) {
              final Map<String, Index> headerIndex = calculateStartingFieldsIndex(output.get(0));
              for (String fields : output.subList(1, output.size())) {
                  machines.add(parse(headerIndex, fields));
              }
          }
  
          return machines;
      }
docs: Executes docker-machine ls --filter field=value command
  
  @param cliPathExec
  location of docker-machine or null if it is on PATH.
  @param field
  to use in condition
  @param value
  value that the field should have
  
  @return set of machines