code: function vowExec(cmd) {
      var defer = vow.defer();
      exec(cmd, function (err, stdout, stderr) {
          if (err) {
              defer.reject({err: err, stderr: stderr});
          } else {
              defer.resolve(stdout.trim());
          }
      });
      return defer.promise();
  }
docs: Runs a command.
  
  @param {String} cmd The command to be run.
  @returns {vow.Promise} Promise that will be fulfilled when the command exits
  with 0 return code and rejected if return code is non-zero.