[SPARK-17614][SQL] sparkSession.read() .jdbc(***) use the sql syntax "where...

[SPARK-17614][SQL] sparkSession.read() .jdbc(***) use the sql syntax "where 1=0" that Cassandra does not support

## What changes were proposed in this pull request?

Use dialect's table-exists query rather than hard-coded WHERE 1=0 query

## How was this patch tested?

Existing tests.

Author: Sean Owen <sowen@cloudera.com>

Closes #15196 from srowen/SPARK-17614.