What this function is actually doing is to create a filesystem,
together with a new partition; for LVM that filesystem could
also be created on a new logical volume though.
The previous commit made sure that `PartitionTable.RootPartition`
is indeed returning the pointer partition object inside the array
of the `PartitionTable`. Thus changes to the returned object will
now directly affect the object and thus there is no need to call
`PartitionTable.updateRootPartition` anymore.
thozza pointed out that `int` is platform dependent which results in
a fs size that is too small for 32-bit machines. This commit changes
the filesystem custimizations to use `uint64` instead of `int`
