code: function createJsonFileDiscoverProvider(hostsFile) {
      var fs = require('fs');
  
      return function jsonFileProvider(callback) {
          fs.readFile(hostsFile, function onFileRead(err, data) {
              if (err) {
                  callback(err);
                  return;
              }
  
              var hosts;
              try {
                  hosts = JSON.parse(data.toString());
              } catch (e) {
                  callback(e);
                  return;
              }
              callback(null, hosts);
              return;
          });
      };
  }
docs: Create a new DiscoverProvider using a host-file.
  @param {string} hostsFile The path to a json file containing an array of strings.
  @returns {DiscoverProvider}