it seems there is a bug in Split

给master发送split命令，master认为对应的ts上已经有split任务在执行了，所以一直delay这个split任务执行，导致split一直没有真正成功。现在用showtsx查看，这个ts仍然任务自己正在执行着一个split任务。但是所有的tablet状态都是Ready的。

Start by examining the master’s handling of the split command and the status reported by showtsx for the affected tablet server (TS). Compare the reported in-progress split task with the Ready state of all tablets; done means a split is no longer delayed when the tablets are Ready and showtsx reports the task state correctly.

Written by the indexing model from the issue text.