ref #673

So you can specify more than one disk

- always install syslinux
- add lvm to runlevel boot
- fix local variable $size
- dont display the /dev/ prefix on disk info

and fix help to include LVM option
ref #592

for dynamic dns

The interfaces should come in order the user configures them and put
lo first of all.

It makes more sense to talk about a system disk and data disk.

We only want fiddle with MBR if we use new disks and not if we install
on a mounted root

So we dont need to ask.

Also fix help message.

If you run 'setup-disk /dev/sda /dev/sdb ...' then automatically set
up raid, even if no -r option was specified. If more than 2 disks
are specified then use raid5, otherwise use raid1.

ask first what disk to use, and then after how to use it.

ref #558

And initial work for data-only disk support.

This reverts commit a04a2d18.