rbd: Don't accept -drive driver=rbd, keyvalue-pairs=...

The way we communicate extra key-value pairs from
qemu_rbd_parse_filename() to qemu_rbd_open() exposes option parameter
"keyvalue-pairs" on the command line.  It's not wanted there.  Hack:
rename the parameter to "=keyvalue-pairs" to make it inaccessible.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Message-id: 1490691368-32099-6-git-send-email-armbru@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>
