create an execution environment with main executorService for fragments execution (can be used as an execution context) and a scheduled executor for timed out execution
the number of executors is set from the arguments.threadsNb value which is Runtime.getRuntime.availableProcessors by default
create an ExecutionEnv from an execution context only
create an ExecutionEnv from Scala global execution context
the number of executors is set from the arguments.scheduledThreadsNb value which is 1 by default