[SPARK-4935][SQL] When hive.cli.print.header configured, spark-sql aborted if passed in a invalid sql

If we passed in a wrong sql like ```abdcdfsfs```, the spark-sql script aborted. 
This line is not triggered because we didn't assign non-zero return code properly before. But now we're using proper return code. Although exceptions and error messages are also caught and reported in other places (e.g. within HiveContext), I still tend to keep this line.