The current implementation in how partition is created for ext2 img
it looks a bit bad.

This patch makes the partition in more standarized way, respecting
cylinder alignement:
* The size of resulting image will be in cylinder multiple ~8MB.
* Use fdisk instead of sfdisk (sfdisk write some bad information)
* Make the result image in one pass, instead of concatenating.

Also the advantage is that with this can add another partitions
without any issues in the usb-flash-drive with this .img.

For example of current situation:

qemu-system-x86_64 -hda archlinux-avr.toolchain.img -serial stdio
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[root@avr ~]# fdisk /dev/sda

Command (m for help): p

Disk /dev/sda: 223 MB, 223974400 bytes
59 heads, 41 sectors/track, 180 cylinders
Units = cylinders of 2419 * 512 = 1238528 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         181      218693+  83  Linux
Partition 1 has different physical/logical beginnings (non-Linux?):
     phys=(0, 1, 1) logical=(0, 1, 23)
Partition 1 has different physical/logical endings:
     phys=(27, 58, 41) logical=(180, 49, 21)

Command (m for help): v
Partition 1 has different physical/logical beginnings (non-Linux?):
     phys=(0, 1, 1) logical=(0, 1, 23)
Partition 1 has different physical/logical endings:
     phys=(27, 58, 41) logical=(180, 49, 21)
Partition 1: previous sectors 437449 disagrees with total 67731
62 unallocated 512-byte sectors

Command (m for help):
---------------------------------------------------------------------

qemu-system-x86_64 -hda archlinux-avr.toolchain-fix.img -serial stdio
---------------------------------------------------------------------
[root@avr ~]# fdisk /dev/sda

Command (m for help): p

Disk /dev/sda: 230 MB, 230307840 bytes
255 heads, 63 sectors/track, 28 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x5c94ca4f

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          28      224878+  83  Linux

Command (m for help): v
62 unallocated 512-byte sectors
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Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>