Couple changes for Linux raid metadata 1.x support

[Doug Nazar]

 Strange timing. I ran into needing support for 1.2 metadata a few days
ago. Wrote the code yesterday and when I pulled to check for conflicts
before I submitted someone else had also just written the code.

Here are a few changes I had that are not in the tree:

- Don't use disks with outdated superblocks
- Don't use disks that are being rebuilt/transfomed
- Check superblock checksums
- Check superblock is in the correct location
- Update the recovery code to use the start_sector

Doug

grub-update-raid-metadata-1x-support.diff
Description: Text document