Increase size of ceph disks to 11G

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 11G
(since journal takes 5GB).

This should fix https://bugzilla.novell.com/show_bug.cgi?id=886795 on
mkcloud.

To use smaller partitions mkcloud would need to prepare the partitions
in advance with "ceph-disk prepare" to set the partitions and journal
directories.