Plugin binary wrappers

[shiqizng]

At this time, to use Conduit we need to define plugin configuration in Conduit.yml and plugins need to be in Conduit repo. It would be nice if Conduit could also run a plugin binary.

processors:
  - name: processor_binary_wrapper
    config:
        path: /path/to/binary

Define IO scheme for passing data to binary.
Different plugins for daemon and one time calls?

Something similar to this:
https://github.com/influxdata/telegraf/tree/master/plugins/processors/execd