Issue description

One request with unhealthy code returned will cause multiple unhealthy HTTP increment if the size of passive.unhealthy.http_statuses is more than 1.

Environment

• apisix version: 2.0
• OS: 3.10.0-693.el7.x86_64
• OpenResty version: openresty/1.17.8.2
• etcd version: 3.4.13
• apisix-dashboard version: 2.0

Minimal test code / Steps to reproduce the issue

The route configuration in etcd is below:

{
	"id": "route_2050210843",
	"create_time": 1618455175,
	"update_time": 1619013202,
	"uris": ["/test1.do"],
	"name": "route-2050210843",
	"desc": "health_check_test",
	"methods": ["GET", "POST", "PUT", "DELETE", "PATCH", "HEAD", "OPTIONS"],
	"vars": [],
	"upstream": {
		"nodes": [{
			"host": "172.25.69.182",
			"port": 8080,
			"weight": 1
		}, {
			"host": "172.25.70.116",
			"port": 8080,
			"weight": 1
		}],
		"timeout": {
			"connect": 6,
			"read": 6,
			"send": 6
		},
		"type": "roundrobin",
		"checks": {
			"active": {
				"healthy": {
					"interval": 100,
					"successes": 10
				},
				"host": "172.25.69.182",
				"http_path": "/check.do",
				"req_headers": [""],
				"timeout": 3,
				"unhealthy": {
					"http_failures": 5,
					"interval": 3
				}
			},
			"passive": {
				"healthy": {
					"http_statuses": [200],
					"successes": 2
				},
				"unhealthy": {
					"http_failures": 5,
					"http_statuses": [500, 502, 504],
					"tcp_failures": 1
				}
			}
		}
	},
	"labels": {
		"serve": "2050210843"
	}
}

1. Set a route with two upstreams and healthcheck active and passive configuration(passive.unhealthy.http_statuses is [500, 502, 504]). One upstream always return 500 and another always return 200.
2. Send a request to trigger creating new checker. It will be passed to the normal upstream.
3. Send a second request, it will be passed to the unnormal upstream.

What's the actual result?

One request with unnormal upstream will cause three times unhealthy HTTP increment.

2021/04/21 21:54:00 [warn] 73450#73450: *3017774 [lua] healthcheck.lua:1142: log(): [healthcheck] (upstream#/apisix/routes/route_2050210843) unhealthy HTTP increment (1/5) for '172.25.69.182(172.25.69.182:8080)' while logging request, client: 10.58.50.104, server: , request: "GET /test1.do HTTP/1.1", upstream: "http://172.25.69.182:8080/test1.do", host: "172.25.71.28:9080"

2021/04/21 21:54:00 [warn] 73450#73450: *3017774 [lua] healthcheck.lua:1142: log(): [healthcheck] (upstream#/apisix/routes/route_2050210843) unhealthy HTTP increment (2/5) for '172.25.69.182(172.25.69.182:8080)' while logging request, client: 10.58.50.104, server: , request: "GET /test1.do HTTP/1.1", upstream: "http://172.25.69.182:8080/test1.do", host: "172.25.71.28:9080"

2021/04/21 21:54:00 [warn] 73450#73450: *3017774 [lua] healthcheck.lua:1142: log(): [healthcheck] (upstream#/apisix/routes/route_2050210843) unhealthy HTTP increment (3/5) for '172.25.69.182(172.25.69.182:8080)' while logging request, client: 10.58.50.104, server: , request: "GET /test1.do HTTP/1.1", upstream: "http://172.25.69.182:8080/test1.do", host: "172.25.71.28:9080"

What's the expected result?

One request with unnormal upstream will cause only once unhealthy HTTP increment.
I cannot understand why it has to be double loop in function healcheck_passive of apisix/init.lua

for i, status in ipairs(http_statuses) do
        for i, status in ipairs(http_statuses) do
            if resp_status == status then
                checker:report_http_status(api_ctx.balancer_ip,
                                           port or api_ctx.balancer_port,
                                           host,
                                           resp_status)
            end
        end
    end