request help: stream proxy healthy check didn't work

[zykgssd]

Issue description

create command:

curl http://127.0.0.1:9080/apisix/admin/stream_routes/1 -H 'X-API-KEY: abcdefgxxxxxxxx' -X PUT -d '
{
    "upstream": {
        "nodes": {
            "22.22.22.22:80": 1,
            "11.11.11.11:80": 1
        },
        "type": "roundrobin",
        "checks": {
            "active": {
                "timeout": 3,
                "http_path": "/healthz",
                "healthy": {
                    "interval": 2,
                    "successes": 1
                },
                "unhealthy": {
                    "interval": 1,
                    "http_failures": 2
                },
                "req_headers": ["User-Agent: curl/7.29.0"]
            },
            "passive": {
                "healthy": {
                    "http_statuses": [200, 201],
                    "successes": 3
                },
                "unhealthy": {
                    "http_statuses": [404, 500],
                    "http_failures": 3,
                    "tcp_failures": 3
                }
            }
        }
    }
}'

`

error.log :
`2020/10/13 15:28:51 [error] 163844#163844: *11181092 failed to run balancer_by_lua*: /usr/local/apisix//deps/share/lua/5.1/resty/healthcheck.lua:1319: please configure the 'lua-resty-worker-events' module before using 'lua-resty-healthcheck'
stack traceback:
	[C]: in function 'assert'
	/usr/local/apisix//deps/share/lua/5.1/resty/healthcheck.lua:1319: in function 'new'
	/usr/local/apisix/apisix/balancer.lua:90: in function 'create_obj_fun'
	/usr/local/apisix/apisix/core/lrucache.lua:95: in function 'lrucache_checker'
	/usr/local/apisix/apisix/balancer.lua:133: in function 'fetch_healthchecker'
	/usr/local/apisix/apisix/balancer.lua:194: in function 'pick_server'
	/usr/local/apisix/apisix/balancer.lua:258: in function 'load_balancer'
	/usr/local/apisix/apisix/init.lua:774: in function 'stream_balancer_phase'
	balancer_by_lua:2: in main chunk while connecting to upstream, client: 10.2.1.9, server: 0.0.0.0:80, bytes from/to client:0/0, bytes from/to upstream:0/0

Environment

• apisix version (cmd: apisix version): 1.5
• OS: CentOS Linux release 7.7.1908 (Core)

[membphis]

that is a todo feature, welcome PR to fix it