code: function execOptionBuilder(options) {
    var validKeys = {
      cwd:        true,
      env:        true,
      encoding:   true,
      shell:      true,
      timeout:    true,
      maxBuffer:  true,
      killSignal: true,
      uid:        true,
      gid:        true
    };
  
    options = options || {};
  
    return Object.keys(options).reduce(function(result, key) {
      if(validKeys[key]) {
        result[key] = options[key];
      }
      return result;
    }, {});
  }
docs: filter passed-in options to get a hash of child process options (i.e., not p4 command arguments)