block/nbd: add cmdline and qapi parameter reconnect-delay

Reconnect will be implemented in the following commit, so for now,
in semantics below, disconnect itself is a "serious error".

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190618114328.55249-5-vsementsov@virtuozzo.com>
[eblake: slipped from 4.1 to 4.2]
Signed-off-by: Eric Blake <eblake@redhat.com>
2 files changed