public ExecutionCommandWrapper getExecutionCommandWrapper(String hostname,
      String role) {
    HostRoleCommand hrc = hostRoleCommands.get(getSafeHost(hostname)).get(role);
    if (hrc != null) {
      return hrc.getExecutionCommandWrapper();
    } else {
      return null;
    }
  }
@param hostname    the hostname; {@code null} for a server-side stage
@param role        the role
@return            the wrapper
ambari-server/src/main/java/org/apache/ambari/server/actionmanager/Stage.java