Hide the default lazy_refcounts=off output from qemu-img like we do with
other image creation options.  This ensures that existing golden outputs
continue to pass despite the new option that has been added.

Note that this patch applies before the one that actually introduces the
lazy_refcounts=on|off option.  This ensures git-bisect(1) continues to
work.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>