Allow users to specify disk numbers in partition configuration spreadsheet

[gregorybruno]

The current implementation requires the user to specify 'sda', 'sdb', etc. for the 'device'.

Let's let the user specify an integer and we'll be able to map the integer to a disk device.

For example, if the user specifies '2' for the device and if the discovered disks are [ 'sda', 'sdb', 'sdc' ] then we'll translate the '2' to 'sdb'.

[culbert]

I would also vote for a device name “any”.