vpc: Fix size in fixed image creation

If total_sectors is rounded to match the geometry, total_size needs to
be changed as well. Otherwise we end up with an image whose geometry
describes a disk larger than the image file, which doesn't end well.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
(cherry picked from commit c7dd631d482912fd615a9ef18a0e0691e7a84836)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>