The following PR exposes beats metrics through a configurable http endpoint. This allows when enabled to get an insight into a running beat. For security reasons the endpoint is off by default.

**Configuration**

The configuration options are in the `http` namespace. This config naming is borrowed from Logstash. By default the http endpoint is disabled. If enabled the metrics are only exposed on localhost on port 5066.

```
http.enabled: false
http.host: localhost
http.port: 5066
```

**-httpprof ?**

The http endpoint can be enabled also in production if needed. The additional endpoint httpprof endpoint which can be enabled through `-httpprof` still exists but is only recommended for debugging purpose. The httpprof endpoint exposes many more metrics and runtime data then the metrics endpoint.

**Endpoints**

The current implementation has two endpoints:

* `/`: The standard endpoint exposes info about the beat
* `/stats`: Stats exposes all metrics collected by monitoring

The output of the data is in json. The flag `?pretty` can be used to have formatted json as output to make it more human readable. Below is an example of each endpoint.

**/**

```
{
  "beat": "metricbeat",
  "hostname": "ruflin",
  "name": "ruflin",
  "uuid": "9d6e0c3a-1677-424c-aead-097e597e09f9",
  "version": "6.0.0-alpha1"
}
```

**/stat**

```
{
  "beat": {
    "memstats": {
      "gc_next": 6262080,
      "memory_alloc": 3879968,
      "memory_total": 479284520
    }
  },
  "libbeat": {
    "config": {
      "module": {
        "running": 0,
        "starts": 0,
        "stops": 0
      },
      "reloads": 0
    }
  },
  "metricbeat": {
    "system": {
      "cpu": {
        "events": 7,
        "failures": 0,
        "success": 7
      },
      "filesystem": {
        "events": 28,
        "failures": 0,
        "success": 7
      },
      "fsstat": {
        "events": 7,
        "failures": 0,
        "success": 7
      },
      "load": {
        "events": 7,
        "failures": 0,
        "success": 7
      },
      "memory": {
        "events": 7,
        "failures": 0,
        "success": 7
      },
      "network": {
        "events": 70,
        "failures": 0,
        "success": 7
      },
      "process": {
        "events": 1324,
        "failures": 0,
        "success": 7
      }
    }
  },
  "output": {
    "elasticsearch": {
      "events": {
        "acked": 1445,
        "not_acked": 0
      },
      "publishEvents": {
        "call": {
          "count": 34
        }
      },
      "read": {
        "bytes": 17213,
        "errors": 0
      },
      "write": {
        "bytes": 1185991,
        "errors": 0
      }
    },
    "events": {
      "acked": 1445
    },
    "kafka": {
      "events": {
        "acked": 0,
        "not_acked": 0
      },
      "publishEvents": {
        "call": {
          "count": 0
        }
      }
    },
    "logstash": {
      "events": {
        "acked": 0,
        "not_acked": 0
      },
      "publishEvents": {
        "call": {
          "count": 0
        }
      },
      "read": {
        "bytes": 0,
        "errors": 0
      },
      "write": {
        "bytes": 0,
        "errors": 0
      }
    },
    "messages": {
      "dropped": 0
    },
    "redis": {
      "events": {
        "acked": 0,
        "not_acked": 0
      },
      "read": {
        "bytes": 0,
        "errors": 0
      },
      "write": {
        "bytes": 0,
        "errors": 0
      }
    },
    "write": {
      "bytes": 1185991,
      "errors": 0
    }
  },
  "publisher": {
    "events": {
      "count": 1450
    },
    "queue": {
      "messages": {
        "count": 1450
      }
    }
  }
}
```

**Questions**

* Are these good endpoints paths?
* Which should be our default port?