qemu: Adjust size for qcow2/qed if not on sector boundary

qemu: Adjust size for qcow2/qed if not on sector boundary

https://bugzilla.redhat.com/show_bug.cgi?id=1002813

If qemuDomainBlockResize() is passed a size not on a KiB boundary - that
is passed a size based in bytes (VIR_DOMAIN_BLOCK_RESIZE_BYTES), then
depending on the source format (qcow2 or qed), the value passed must
be on a sector (or 512 byte) boundary. Since other libvirt code quietly
adjusts the capacity values, then do so here as well - of course ensuring
that adjustment still fits.

Signed-off-by: John Ferlan <jferlan@redhat.com>