Ensure blkid FS_Info cache has entries for all whole disk devices (#771244)

More recent versions of blkid don't report an ISO9660 file system on the
whole disk device if partitions can be reports for embedded partitions.
However when querying the whole disk device directly then the expected
ISO9660 file system is reported.  For example on CentOS 7 with the
previous ISO images:

    # wget http://git.kernel.org/cgit/utils/util-linux/util-linux.git/plain/tests/ts/isosize/sample.iso.gz
    # dd if=/dev/zero bs=1M of=/dev/sdc
    # zcat sample.iso.gz | dd of=/dev/sdc

    # blkid -v
    blkid from util-linux 2.23.2  (libblkid 2.23.0, 25-Apr-2013)
    # blkid | fgrep /dev/sdc
    /dev/sdc1: UUID="2013-01-04-22-05-45-00" LABEL="ARCH_201301" TYPE="iso9660" PTTYPE="dos"
    # blkid /dev/sdc
    /dev/sdc: UUID="2013-01-04-22-05-45-00" LABEL="ARCH_201301" TYPE="iso9660" PTTYPE="dos"

    # wget http://cdimage.debian.org/debian-cd/8.6.0/amd64/iso-cd/debian-8.6.0-amd64-netinst.iso
    # dd if=/dev/zero bs=1M of=/dev/...