New mkfs.vfat and fatlabel tools included in the dosfsutils package no
longer support creating vfat disks with lowercase labels. They silently
default to an all uppercase label eg CONFIG-2 instead of config-2. This
change makes cloud-init handle either upper or lower case.
Change-Id: Iec927db04b9621b20c9bee2c8d81325d7af80f9b
Closes-Bug: #1598783