[TEST] initialize SUITE | GLOBAL scope cluster in a private random context

Today any call to the current randomized context modifies the random
sequence such that cluster initialization is context dependent. If due
to an error for instance a static util method is used like `randomLong`
inside the TestCluster instead of the provided Random instance all
reproducibility guarantees are gone. This commit adds a safe mechanism
to initialize these clusters even if a static helper is used. All none
test scope clusters are now initialized in a private randomized context.
Could this be moved out to a method of it's own and just called from this anonymous inner? It is just a bit unwieldy (at least in the review) looking at something so deeply nested. I think just having a private static that takes the seed would work?