code: function _performInstall(packagePath, installDirectory, validationResult, callback) {
      validationResult.installedTo = installDirectory;
  
      function fail(err) {
          _removeFailedInstallation(installDirectory);
          callback(err, null);
      }
  
      function finish() {
          // The status may have already been set previously (as in the
          // DISABLED case.
          if (!validationResult.installationStatus) {
              validationResult.installationStatus = Statuses.INSTALLED;
          }
          callback(null, validationResult);
      }
  
      fs.mkdirs(installDirectory, function (err) {
          if (err) {
              callback(err);
              return;
          }
          var sourceDir = path.join(validationResult.extractDir, validationResult.commonPrefix);
  
          fs.copy(sourceDir, installDirectory, function (err) {
              if (err) {
                  return fail(err);
              }
              finish();
          });
      });
  }
docs: Private function to unzip to the correct directory.
  
  @param {string} Absolute path to the package zip file
  @param {string} Absolute path to the destination directory for unzipping
  @param {Object} the return value with the useful information for the client
  @param {Function} callback function that is called at the end of the unzipping