private Set<String> getHostList(Map<String, String> cmdParameters, String key) {
    Set<String> hosts = new HashSet<>();
    if (cmdParameters.containsKey(key)) {
      String allHosts = cmdParameters.get(key);
      if (allHosts != null) {
        for (String hostName : allHosts.trim().split(",")) {
          hosts.add(hostName.trim());
        }
      }
    }
    return hosts;
  }
Creates and populates service check EXECUTION_COMMAND for host. Not all
EXECUTION_COMMAND parameters are populated here because they are not needed
by service check.
ambari-server/src/main/java/org/apache/ambari/server/controller/AmbariCustomCommandExecutionHelper.java