BZ-1012367 - Deployment of Business-central to cluster fails on AppSetup...

....assertPlayground()

allows to control the clustered IO service by actually starting its communication part (connecting to cluster and send/receive messages). When autoStart is disabled clustered IO service acts as regular IOService making the changes only locally.

the main reason for providing this option is to be able to create whatever is required in advance before the cluster part comes into the picture. A perfect example is kie-wb startup that in case of fresh installation bootstraps demo repositories and in clustered environment all cluster members do the same which causes number of issues (FileSystemAlreadyExists to name one) due to cluster has already propagated changes to other nodes.
With this application can enable/start the cluster capabilities once it's ready meaning when the bootstrap is completed. Since the work is done on all cluster members it won't have any side effects like missing commits etc.

By default the "autoStart" feature is enabled so it does work same way as now. Then application will need to do the extra work to disable autoStart and then starting it manually when it's ready.