[SPARK-20218][DOC][APP-ID] applications//stages' in REST API,add description.

## What changes were proposed in this pull request?

1. '/applications/[app-id]/stages' in rest api.status should add description '?status=[active|complete|pending|failed] list only stages in the state.'

Now the lack of this description, resulting in the use of this api do not know the use of the status through the brush stage list.

2.'/applications/[app-id]/stages/[stage-id]' in REST API,remove redundant description ‘?status=[active|complete|pending|failed] list only stages in the state.’.
Because only one stage is determined based on stage-id.

code:
  GET
  def stageList(QueryParam("status") statuses: JList[StageStatus]): Seq[StageData] = {
    val listener = ui.jobProgressListener
    val stageAndStatus = AllStagesResource.stagesAndStatus(ui)
    val adjStatuses = {
      if (statuses.isEmpty()) {
        Arrays.asList(StageStatus.values(): _*)
      } else {
        statuses
      }
    };

## How was this patch tested?

manual tests

Please review http://spark.apache.org/contributing.html before opening a pull request.

Author: 郭小龙 10207633 <guo.xiaolong1@zte.com.cn>

Closes #17534 from guoxiaolongzte/SPARK-20218.