Add testcase for exFAT that currently fails

Disk image obtained from:
http://www.cfreds.nist.gov/dfr-images/dfr-01-xfat.dd.bz2 -- was ripped off the
first GPT partition and verified to be a FAT-like partition with file(1)/hexdump.

This testcase currently fails

PR: 214908
Sponsored by: Dell EMC Isilon