stress: fix SQLite support and make it usable even if MySQLdb is not installed

neo/tests/__init__.py

@@ -26,7 +26,6 @@ import sys
 import tempfile
 import unittest
 import weakref
-import MySQLdb
 import transaction
 
 from contextlib import contextmanager
@@ -141,6 +140,7 @@ def getTempDirectory():
 def setupMySQLdb(db_list, clear_databases=True):
     if mysql_pool:
         return mysql_pool.setup(db_list, clear_databases)
+    import MySQLdb
     from MySQLdb.constants.ER import BAD_DB_ERROR
     user = DB_USER
     password = ''
@@ -178,6 +178,7 @@ class MySQLPool(object):
         self.kill(*self._mysqld_dict)
 
     def setup(self, db_list, clear_databases):
+        import MySQLdb
         start_list = set(db_list).difference(self._mysqld_dict)
         if start_list:
             start_list = sorted(start_list)

neo/tests/functional/__init__.py

@@ -22,7 +22,6 @@ import ZODB
 import socket
 import signal
 import random
-import MySQLdb
 import sqlite3
 import unittest
 import tempfile

tools/stress

@@ -650,11 +650,14 @@ def main():
             parser.error(
                 '--datadir: meaningless when using an existing MySQL server')
 
+    kw = {'wait': -1}
+    if args.engine:
+        kw['engine'] = args.engine
     kw = dict(db_list=db_list, name='stress',
         partitions=args.partitions, replicas=args.replicas,
         adapter=args.adapter, address_type=args.address_type,
         temp_dir=args.logdir or args.datadir or getTempDirectory(),
-        storage_kw={'engine': args.engine, 'wait': -1})
+        storage_kw=kw)
 
     if args.command == 'run':
         NFQueue.delay = args.delay