"java.lang.OutOfMemoryError: unable to create native thread" when trying to run 6K clients test [DEX-371]

[ihsandemir]

When trying to run 6K clients test, we hit the following error:

[42.559s][warning][os,thread] Failed to start thread "Unknown thread" - pthread_create failed (EAGAIN) for attributes: stacksize: 2048k, guardsize: 16k, detached.
[42.559s][warning][os,thread] Failed to start the native thread for java.lang.Thread "createWorkers-Thread-3812"
Exception in thread "main" 
java.lang.OutOfMemoryError: unable to create native thread: possibly out of memory or process/resource limits reached
Acceptance Criteria

• 6K clients test can be run successfully
• 12K clients test can be run successfully

https://hazelcast.atlassian.net/browse/DEX-371