Deduplicate the task result that generated by more branches in union all

HIVE-23891 adds the ability to deduplicate the task result that under the directory,

<table-dir>/<staging-dir>/_tmp.-ext-10000/<dynamic-partition-dir>/HIVE_UNION_SUBDIR_1,

but turns out to ignore taking the same action to the output directory for the same query:

<table-dir>/<staging-dir>/_tmp.-ext-10000/<dynamic-partition-dir>/HIVE_UNION_SUBDIR_2.

So user may still have the same data duplication problem upon multiple tez task attempts.