[SPARK-16538][SPARKR] Add more tests for namespace call to SparkSession functions

## What changes were proposed in this pull request?

More tests
I don't think this is critical for Spark 2.0.0 RC, maybe Spark 2.0.1 or 2.1.0.

## How was this patch tested?

unit tests

shivaram dongjoon-hyun

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #14206 from felixcheung/rroutetests.