[SPARK-15929] Fix portability of DataFrameSuite path globbing tests

The DataFrameSuite regression tests for SPARK-13774 fail in my environment because they attempt to glob over all of `/mnt` and some of the subdirectories restrictive permissions which cause the test to fail.

This patch rewrites those tests to remove all environment-specific assumptions; the tests now create their own unique temporary paths for use in the tests.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #13649 from JoshRosen/SPARK-15929.