Currently dmsquash-live-root requires that squashfs images be named
"squashfs.img" and all others be "ext3fs.img" or "rootfs.img".
If we've got a live image in initramfs, this patch will make dracut use
losetup and det_fs to determine the actual filesystem type of the image.
Signed-off-by: Will Woods <wwoods@redhat.com>