Support machine-friendly output formats about rabbitmq-cli

[michaelklishin]

Partially addressed by #90.

[michaelklishin]

Further addressed by #115.

[michaelklishin]

FWIW the core of multi-format support is there. We are not 100% happy with the state of things at the moment but there's only so much time left in the 3.7.0 cycle. Considering this closed with further improvements we have in mind.

[visbits]

So how about this now..

[michaelklishin]

@visbits if there's a question, consider asking on the mailing list.

Some commands support --formatter=json, possibly even --formatter=csv. It doesn't make sense for all commands and in some cases the output could be formatted much better. We've concluded that we want to support multiple formatters better but there's a fair amount of command-specific work and we have close to 100 commands now. So the degree of support varies and for some commands, only one formatter is supported by design.

Here are some examples with 3.7.13:

rabbitmqctl list_vhosts --formatter=json | jq
[
  {
    "name": "/"
  }
]

rabbitmqctl list_users --formatter=json | jq
[
  {
    "user": "guest",
    "tags": [
      "administrator"
    ]
  }
]

rabbitmqctl list_parameters --formatter=json | jq
[
  {
    "component": "federation-upstream",
    "name": "up-hare",
    "value": "{\"expires\":3600000,\"uri\":\"amqp://localhost:5673\"}"
  }
]

rabbitmqctl list_queues --formatter=json | jq
[
  {
    "name": "q1",
    "messages": 0
  },
  {
    "name": "amq.gen-IdssHRoMD4umuqnuHCGdaQ",
    "messages": 0
  }
]

rabbitmqctl list_consumers --formatter=json | jq
[
  {
    "queue_name": "amq.gen-IdssHRoMD4umuqnuHCGdaQ",
    "channel_pid": "#PID<10132.853.0>",
    "consumer_tag": "bunny-1552068127000-449053712679",
    "ack_required": false,
    "prefetch_count": 0,
    "arguments": []
  }
]

rabbitmq-diagnostics listeners --formatter=json | jq
{
  "listeners": [
    {
      "interface": "[::]",
      "node": "rabbit@warp10",
      "port": 25672,
      "protocol": "clustering",
      "purpose": "inter-node and CLI tool communication"
    },
    {
      "interface": "[::]",
      "node": "rabbit@warp10",
      "port": 5672,
      "protocol": "amqp",
      "purpose": "AMQP 0-9-1 and AMQP 1.0"
    },
    {
      "interface": "[::]",
      "node": "rabbit@warp10",
      "port": 5671,
      "protocol": "amqp/ssl",
      "purpose": "AMQP 0-9-1 and AMQP 1.0 over TLS"
    },
    {
      "interface": "[::]",
      "node": "rabbit@warp10",
      "port": 15672,
      "protocol": "http",
      "purpose": "HTTP API"
    },
    {
      "interface": "[::]",
      "node": "rabbit@warp10",
      "port": 15671,
      "protocol": "https",
      "purpose": "HTTP API over TLS (HTTPS)"
    },
    {
      "interface": "[::]",
      "node": "rabbit@warp10",
      "port": 1883,
      "protocol": "mqtt",
      "purpose": "MQTT"
    }
  ],
  "result": "ok"
}

rabbitmq-diagnostics alarms --formatter=json | jq
{
  "alarms": [],
  "node": "rabbit@warp10",
  "result": "ok"
}