Correctly register autoloading before install.php and loading commands

lib/private/Console/Application.php

 					if($appPath === false) {
 						continue;
 					}
-					\OC::$loader->addValidRoot($appPath);
+					\OC_App::registerAutoloading($app, $appPath);
 					$file = $appPath . '/appinfo/register_command.php';
 					if (file_exists($file)) {
 						require $file;

lib/private/Installer.php

 		}
 
 		//run appinfo/install.php
-		\OC::$loader->addValidRoot($appPath);
+		\OC_App::registerAutoloading($app, $appPath);
 		self::includeAppScript("$appPath/appinfo/install.php");
 
 		$info = OC_App::getAppInfo($app);

lib/private/legacy/app.php

 	}
 
 	/**
+	 * @internal
 	 * @param string $app
 	 * @param string $path
 	 */
-	protected static function registerAutoloading($app, $path) {
+	public static function registerAutoloading($app, $path) {
 		// Register on PSR-4 composer autoloader
 		$appNamespace = \OC\AppFramework\App::buildAppNamespace($app);
 		\OC::$composerAutoloader->addPsr4($appNamespace . '\\', $path . '/lib/', true);

tests/settings/controller/EncryptionControllerTest.php

 
 	public function testStartMigrationSuccessful() {
 		// we need to be able to autoload the class we're mocking
-		\OC::$loader->addValidRoot(\OC_App::getAppPath('encryption'));
+		\OC_App::registerAutoloading('encryption', \OC_App::getAppPath('encryption'));
 
 		$migration = $this->getMockBuilder('\\OCA\\Encryption\\Migration')
 			->disableOriginalConstructor()->getMock();