[SPARK-21648][SQL] Fix confusing assert failure in JDBC source when parallel...

[SPARK-21648][SQL] Fix confusing assert failure in JDBC source when parallel fetching parameters are not properly provided.

### What changes were proposed in this pull request?
```SQL
CREATE TABLE mytesttable1
USING org.apache.spark.sql.jdbc
  OPTIONS (
  url 'jdbc:mysql://${jdbcHostname}:${jdbcPort}/${jdbcDatabase}?user=${jdbcUsername}&password=${jdbcPassword}',
  dbtable 'mytesttable1',
  paritionColumn 'state_id',
  lowerBound '0',
  upperBound '52',
  numPartitions '53',
  fetchSize '10000'
)
```

The above option name `paritionColumn` is wrong. That mean, users did not provide the value for `partitionColumn`. In such case, users hit a confusing error.

```
AssertionError: assertion failed
java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:156)
	at org.apache.spark.sql.execution.datasources.jdbc.JdbcRelationProvider.createRelation(JdbcRelationProvider.scala:39)
	at org.apache.spark.sql.execution.datasources.DataSource.resolveRelation(DataSource.scala:312)
```

### How was this patch tested?
Added a test case

Author: gatorsmile <gatorsmile@gmail.com>

Closes #18864 from gatorsmile/jdbcPartCol.