mysql: fix deprecated storage_engine variable (allegro#2944)

storage_engine variable has been deprecated in MySQL 5.5.
default_storage_engine is a substitution

fixes compatibility with MySQL 5.7

src/ralph/settings/base.py

@@ -121,7 +121,7 @@ def str_to_bool(s: str) -> bool:
     'sql_mode': 'TRADITIONAL',
     'charset': 'utf8',
     'init_command': """
-    SET storage_engine=INNODB;
+    SET default_storage_engine=INNODB;
     SET character_set_connection=utf8,collation_connection=utf8_unicode_ci;
     SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
     """