DRILL-6197: Skip duplicate entry for OperatorStats
org.apache.drill.exec.ops.FragmentStats should skip injecting the org.apache.drill.exec.ops.OperatorStats instance for these operators:
org.apache.drill.exec.proto.beans.CoreOperatorType.SCREEN
org.apache.drill.exec.proto.beans.CoreOperatorType.SINGLE_SENDER
org.apache.drill.exec.proto.beans.CoreOperatorType.BROADCAST_SENDER
org.apache.drill.exec.proto.beans.CoreOperatorType.HASH_PARTITION_SENDER
closes #1141
