SPARK-4506 [DOCS] Addendum: Update more docs to reflect that standalone works in cluster mode

This is a trivial addendum to SPARK-4506, which was already resolved. noted by Asim Jalis in SPARK-4506.

Author: Sean Owen <sowen@cloudera.com>

Closes #4160 from srowen/SPARK-4506 and squashes the following commits:

5f5f7df [Sean Owen] Update more docs to reflect that standalone works in cluster mode