Merge pull request #6072 from owncloud/mssql-fix-schema-migration-oc6

on mssql the schema migration sometimes fails due to an already existing...

lib/private/db/mdb2schemamanager.php

@@ -19,6 +19,8 @@ class MDB2SchemaManager {
 	 */
 	public function __construct($conn) {
 		$this->conn = $conn;
+		$this->conn->close();
+		$this->conn->connect();
 	}
 
 	/**