Fix data stream retrieval in DataStreamLifecycleServiceIT (elastic#125195)

These tests had the potential to fail when two consecutive GET data
streams requests would hit two different nodes, where one node already
had the cluster state that contained the new backing index and the other
node didn't yet.

Caused by elastic#122852

Fixes elastic#124846
Fixes elastic#124950
Fixes elastic#124999

Author: nielsbauman