Increases priority of configuration getter thread in cluster tests

Adds optional priority argument in NamedThreadFactory constructor
Uses that to have the configuration getter thread in ClusterMockTest run with highest prio
This is necessary for windows tests to pass on CI
Adds timed wait on ResponseFuture so it is more frequently scheduled
RelationshipChainExplorerTest properly shuts down StoreAccess
Sets realistic configuration in ClusterMembershipTest