Fix MySQL 8.0+ compatibility

In MYSQL 8.0 one cannot create users using GRANT.
https://dev.mysql.com/doc/refman/8.0/en/mysql-nutshell.html#mysql-nutshell-removals
(MariaDB worked fine)

warden_server/test_warden_server.py

@@ -413,7 +413,8 @@ def init_user():
     try:
         conn = my.connect(user='root', passwd=getpass.getpass('Enter MySQL Root password:'))
         with conn.cursor() as cur:
-            cur.execute("GRANT SELECT, INSERT, UPDATE, CREATE, DELETE, DROP ON *.* TO %s@'localhost' IDENTIFIED BY %s", (USER, PASSWORD))
+            cur.execute("CREATE USER IF NOT EXISTS %s@'localhost' IDENTIFIED BY %s", (USER, PASSWORD))
+            cur.execute("GRANT SELECT, INSERT, UPDATE, CREATE, DELETE, DROP ON *.* TO %s@'localhost'", (USER,))
         conn.commit()
         print("DB User set up successfuly")
     except my.OperationalError as ex: