qapi: add name parameter to nbd-server-add

Allow user to specify name for new export, to not reuse internal
node name and to not show it to clients.

This also allows creating several exports per device.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180119135719.24745-2-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
3 files changed