Ohai Target Mode aka Remote Ohai

[lamont-granquist]

This implements remote ohai, inspired originally by http://github.com/burtlo/ohbye

1. When targeting remote unix-like or windows systems it preserves the semantics of ohai run locally (apart from a few known bugs)
2. It implements a "train" plugin with data in node['train'] about the remote connection
3. For non-unix/windows systems it disables most default plugins other than os, ohai_time + chef_version, and introduces a :target type which is the default that is used for those kinds of targets
4. It supports URLs in the --target option on the command line and also uses chef-client's code for parsing credentials files
5. With the chef-client PR this integrates seamlessly with chef-client
6. Existing plugins have been converted to use the train helpers to enable remote collection (mostly)

Adds train data to ohai when running remotely:

  "train": {
    "family_hierarchy": [
      "debian",
      "linux",
      "unix",
      "os"
    ],
    "family": "debian",
    "platform": {
      "arch": "x86_64",
      "release": "18.04"
    },
    "backend": "unknown",
    "scheme": "ssh",
    "uri": "ssh://root@crash.scriptkiddie.org:747"
  },

[phiggins]

I'm impressed at the number of different ways in this repo to open a file and read each line.