Fix regression introduced in <42fd5a58>. With q35 machine type which
requires the explicitly specified FDC we'd format twoisa-fdc
controllers to the command line as the code was moved to a place where
it's called per-disk.

Move the call back after formatting all disks and reiterate the disks to
find the floppy controllers.

This also moves the '-global' directive which sets up the default
ISA-FDC to the end after all the disks but since we are modifying the
properties it is safe to do so.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>