Support HealtchCheck on tcp layer，avoid to produce needless http access log

[shi7161979]

local ok, err = hc.spawn_checker{ shm = "healthcheck", -- defined by "lua_shared_dict" upstream = "foo.com", -- defined by "upstream" type = "tcp", interval = 2000, -- run the check cycle every 2 sec timeout = 1000, -- 1 sec is the timeout for network operations fall = 3, -- # of successive failures before turning a peer down rise = 2, -- # of successive successes before turning a peer up concurrency = 10, -- concurrency level for test requests }

[shi7161979]

update error message ，thank you for your suggestion， Tieske。

[Colstuwjx]

why we don't merge this? @Tieske

[Tieske]

@Colstuwjx I commented on it, but I'm not a maintainer of this lib

[timebug]

+1 ping @thibaultcha @spacewander