[SPARK-18989][SQL] DESC TABLE should not fail with format class not found

## What changes were proposed in this pull request?

When we describe a table, we only wanna see the information of this table, not read it, so it's ok even if the format class is not present at the classpath.

## How was this patch tested?

new regression test

Author: Wenchen Fan <wenchen@databricks.com>

Closes #16388 from cloud-fan/hive.