Serve broker diagnostics over HTTP

[otoolep]

Add diagnostic endpoint to broker.

[otoolep]

Example output:

{
    "isLeader": true,
    "clusterID": 2845091057032640500,
    "path": "/home/philip/.influxdb/broker",
    "index": 22,
    "topics": {
        "/home/philip/.influxdb/broker/0": {
            "id": 0,
            "path": "/home/philip/.influxdb/broker/0",
            "open": true,
            "truncated": false,
            "index": 17,
            "indexByURL": {
                "http://localhost:8086": 17
            },
            "maxSegmentSize": 10485760
        },
        "/home/philip/.influxdb/broker/1": {
            "id": 1,
            "path": "/home/philip/.influxdb/broker/1",
            "open": true,
            "truncated": false,
            "index": 18,
            "indexByURL": {
                "http://localhost:8086": 18
            },
            "maxSegmentSize": 10485760
        }
    },
    "maxTopicSize": 52428800
}

[otoolep]

These numbers will allow us to determine how many messages have been written to each broker, and where each subscriber is within each topic.

[toddboom]

+1