xenapi: ephemeral disk partition should fill disk

The current code looks to specify the expected start and finish values
for the partition. A unit miss match between what nova and parted count
as a GB seem to cause the difference.

As we just want to fill the whole disk, we can pass "-0" as the end
value, to tell parted to extend the partition to the end of the disk.

Fixes bug 1241734
Change-Id: Ie4753d9de1e20561b8f96360e879075498a5ef58
Merge "xenapi: ephemeral disk partition should fill disk"