Indexing failures have caused the reindex http request to fail for a while
now. Both search and indexing failures cause it to abort. But search
failures didn't cause a non-200 response code from the http api. This
fixes that.
Also slips in a fix to some infrequently failing rest tests.
Closes#16037
All we do is check the cancelled flag and stop the request at a few key
points.
Adds the cancellation cause to the status so any request that is cancelled
but doesn't die can be seen in the task list.
This creates an reindex plugin with a very basic implementation that is
very like delete-by-query. New we'll integrate it with the task managament
work but for now this works.
Nik Everett