code: public BasicSebConfiguration addSystemPropertiesBefore(String beforeKey) {
  		return (BasicSebConfiguration) addPropertiesBefore(beforeKey, SYSTEM_PROPERTIES_KEY, System.getProperties());
  	}
docs: Adds {@link System#getProperties()} before specific key in actual
  properties list.
  
  @param beforeKey
  The before properties key
  @return Same instance