Implements CompositeIndicesRequest on UpdateByQueryRequest and
ReindexRequest so that plugins can reason about the request. In both cases
this implementation is imperfect but useful because instead of listing
all requests that make up the request it instead attempts to make dummy
requests that represent the requests that it will later make.
_wait_for_completion defaults to false. If set to true then the API will
wait for all the tasks that it finds to stop running before returning. You
can use the timeout parameter to prevent it from waiting forever. If you
don't set a timeout parameter it'll default to 30 seconds.
Also adds a log message to rest tests if any tasks overrun the test. This
is just a log (instead of failing the test) because lots of tasks are run
by the cluster on its own and they shouldn't cause the test to fail. Things
like fetching disk usage from the other nodes, for example.
Switches the request to getter/setter style methods as we're going that
way in the Elasticsearch code base. Reindex is all getter/setter style.
Closes#16906
Boaz Leskes
Nik Everett
Adrien Grand