[SPARK-18545][SQL] Verify number of hive client RPCs in PartitionedTablePerfStatsSuite

## What changes were proposed in this pull request?

This would help catch accidental O(n) calls to the hive client as in https://issues.apache.org/jira/browse/SPARK-18507

## How was this patch tested?

Checked that the test fails before https://issues.apache.org/jira/browse/SPARK-18507

 was patched. cc cloud-fan

Author: Eric Liang <ekl@databricks.com>

Closes #15985 from ericl/spark-18545.

(cherry picked from commit 85235ed6)
Signed-off-by: Wenchen Fan <wenchen@databricks.com>