For some machine types ppc64 machines now require that memory sizes are
aligned to 256MiB increments (due to the dynamically reconfigurable
memory). As now we treat existing configs reasonably in regards to
migration, we can round all the sizes unconditionally. The only drawback
will be that the memory size of a VM can potentially increase by
(256MiB - 1byte) * number_of_NUMA_nodes.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1249006