ISPN-4802 Make HotRodConcurrentStartTest more robust

* Since the method starts Hot Rod servers, it should take responsibility to kill them too.
* Increased timeout for creating Hot Rod server.
* Use fork() method so that thread naming is correctly set.
* Finally, use Try() as a cleaner way to deal with failures of either of Hot Rod server startups.
Given the test defines a variable ```numberOfServers```, maybe the test could be more dynamic:
```
 val futures: Seq[Future[HotRodServer]] = (1 to numberOfServers).map { 
    case 1 =>  // Start first server with delay
    case i =>  // Start other server(s)
}
```