[fedora-arm] Preparing Fedora 25 for Chromebook fails

Following the instructions at https://fedoraproject.org/wiki/Architectures/ARM/Chromebook,
I have encountered this issue. I use the default workstation build (I guess it's
Gnome) instead of an spin here, however I have tested all the spins and they fail to build
also. Basically the fs seems to be corrupt:

```sh
$ cd /var/tmp
```

```sh
$ wget
http://download.fedoraproject.org/pub/fedora/linux/releases/25/Workstatio...
```

Unpack the archive

```sh
$ unxz -v -k Fedora-Workstation-armhfp-25-1.3-sda.raw.xz
```

Next you mount the raw disk image

```sh
$ sudo kpartx -av /var/tmp/Fedora-Workstation-armhfp-25-1.3-sda.raw
```

The device mapping output:

```sh
add map loop0p1 (253:4): 0 59392 linear /dev/loop0 2048
add map loop0p2 (253:5): 0 999424 linear /dev/loop0 61440
add map loop0p3 (253:6): 0 999424 linear /dev/loop0 1060864
add map loop0p4 (253:7): 0 10741760 linear /dev/loop0 2060288
```

Extract the root file system

```sh
$ sudo dd if=/dev/mapper/loop0p3 of=/var/tmp/Fedora-25-Workstation-rootfs.ext4 conv=fsync
status=progress
```

Delete the raw disk image mappings

```sh
$ sudo kpartx -d /var/tmp/Fedora-Workstation-armhfp-25-1.3-sda.raw
```

Check the root file system copy

```sh
$ sudo e2fsck -f /var/tmp/Fedora-25-Workstation-rootfs.ext4
```

e2fsck fails, error message

```sh
e2fsck 1.43.1 (08-Jun-2016)
ext2fs_open2: Bad magic number in super-block
e2fsck: Superblock invalid, trying backup blocks...
e2fsck: Bad magic number in super-block while trying to open
/var/tmp/Fedora-25-Workstation-rootfs.ext4

The superblock could not be read or does not describe a valid ext2/ext3/ext4
filesystem.  If the device is valid and it really contains an ext2/ext3/ext4
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>
 or
    e2fsck -b 32768 <device>

/var/tmp/Fedora-25-Workstation-rootfs.ext4 contains a swap file system labelled
'_swap'
```