public long getStartTime(String hostname, String role) {
    return hostRoleCommands.get(getSafeHost(hostname)).get(role).getStartTime();
  }
@param hostname    the hostname; {@code null} for a server-side stage
@param role        the role
@return the start time for the task
ambari-server/src/main/java/org/apache/ambari/server/actionmanager/Stage.java