Increase size of ceph disks to 10G

To compute the default weight of the disks, ceph is doing something like:

df -P -k $disk | tail -1 | awk '{ print sprintf("%.2f",$2/1073741824) }'

This gives 0.00 unless the disk is bigger than ~5.5G.

Per recommendation of storage people, just increase the default to 10G.
This should fix https://bugzilla.novell.com/show_bug.cgi?id=886795 on
mkcloud.