[SPARK-3547]Using a special exit code instead of 1 to represent ClassNotFoundExcepti...

...on

As improvement of https://github.com/apache/spark/pull/1944, we should use more special exit code to represent ClassNotFoundException.
Ah, good point! The integer is converted to an unsigned byte under bash. And for 1024, the converted value is actually 0, which is definitely not acceptable... Maybe some prime number like 251 instead?