The docs talked about an active snapshot when they meant an active
domain; they also claimed the flag was a no-op for hypervisors with no
snapshot metadata even though the flag is currently rejected as
unrecognized for hypervisors with no snapshot support at all.  A later
patch may teach more drivers to ignore the flag as a no-op, but that
shouldn't conflict with the wording chosen here (since a new client
talking to an old server still runs into the same issue, even if a
newer server becomes more tolerant).
Reported-by: NPeter Krempa <pkrempa@redhat.com>
Signed-off-by: NEric Blake <eblake@redhat.com>
Acked-by: NPeter Krempa <pkrempa@redhat.com>