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.
Minor comment:

If you define an implicit ExecutionContext in your scope, you can delegate to fork:
```
implicit val whatever = new ExecutionContext {
     def execute(runnable: Runnable) {
         fork(runnable)
     }
 }
```
and then avoid the java verbosiness:
```
val future1 = Future(
     startHotRodServerWithDelay(getCacheManagers.get(0), initialPort, 10000)
)
```