[TEST] Stabelize SimpleRecoveryLocalGatewayTests#testReusePeerRecovery
[TEST] Remove unused plugin isolation leftover
[Tests] add different node name prefix for the different cluster type

During a test run we have a global shared cluster and potentially a suite level or even a test level cluster running. All of those share the same node name pattern (node_#). This can be confusing if you're debugging discovery related tests where those nodes from the different clusters potentially interact (and reject each other). This commit gives each cluster type a unique prefix to make tracing and log filtering simpler.

Closes #7518
Aggregations: The nested aggregator should iterate over the child doc ids in ascending order.

The reverse_nested aggregator requires that the emitted doc ids are always in ascending order, which is already enforced on the scorer level,
but this also needs to be enforced on the nested aggrgetor level otherwise incorrect counts are a result.

Closes #7505
Closes #7514