remove plugin_type

[nrdmn]

This PR removes the plugin_type feature in #80 because it is redundant and because its current implementation breaks when there are no inputs or outputs.

[yankcrime]

Thanks.

[sparr]

I think the removed code here was also breaking the new functionality for having two copies of the same input in an array. The exec example from the readme didn't work, and I've been pulling my hair out for a couple of days tracking down the problem to the conf template's pre-manipulation of the inputs array.

[hanej]

@nrdmn, @yankcrime, or @sparr

99% of our systems send metrics to RabbitMQ so we have a global configuration set to use the amqp output. The only systems that don't need these outputs are the ones that pull metrics off of the queues to insert into the database. This was the other major reason for plugin_type.

In our global configuration we have something like this:

telegraf::outputs:
  amqp:
    - brokers: ["amqp://user:pass@rabbitmq:5672/metrics"]
      exchange: 'exch.influxdb.app'
      exchange_type: 'x-consistent-hash'
      exchange_passive: true
      exchange_durability: ""
      routing_tag: '#'
      delivery_mode: "persistent"
      timeout: "10s"
      data_format: 'influx'
      namedrop:
        - 'access_log'
      tagdrop:
        influxdb_database: ["docker", "events", "f5", "rabbitmq", "telegraf", "postfix", "velocity", "vmware"]
  amqp-log:
    - plugin_type: 'amqp'
      brokers: ["amqp://user:pass@rabbitmq:5672/metrics"]
      exchange: 'exch.influxdb.log'
      exchange_type: 'x-consistent-hash'
      exchange_passive: true
      exchange_durability: ""
      routing_tag: '#'
      delivery_mode: "persistent"
      timeout: "10s"
      data_format: 'influx'
      namepass:
        - 'access_log'
  amqp-sys:
    - plugin_type: 'amqp'
      brokers: ["amqp://user:pass@rabbitmq:5672/metrics"]
      exchange: 'exch.influxdb.sys'
      exchange_type: 'x-consistent-hash'
      exchange_passive: true
      exchange_durability: ""
      routing_tag: '#'
      delivery_mode: "persistent"
      timeout: "10s"
      data_format: 'influx'
      tagpass:
        influxdb_database: ["docker", "events", "f5", "rabbitmq", "telegraf", "postfix", "velocity", "vmware"]

Then in other configurations we can easily exclude the specific outputs we don't want to use.

telegraf::outputs:
  amqp:
    - plugin_ensure: 'absent'
  amqp-log:
    - plugin_ensure: 'absent'
  amqp-sys:
    - plugin_ensure: 'absent'

With this merge removing that ability, is there an alternative way to exclude specific configurations from a deep-merged hiera config? I've been using this configuration for several years now without issue so I'd be very interested to hear any problems that it caused.