MySQLdb doesn't allow None to be passed for password

[Rick Harris]

Received this traceback: http://paste.openstack.org/show/2209/

The root cause seems to be that SQLAlchemy's `make_url` will return None if the password isn't present. When we try to pass this `None` value to the MySQLdb driver, it complains since it's expecting a string.

The fix here is to do something like:

connection_dict.password or ''

After testing that out, it seems to fix the problem.

Notes:

>>> MySQLdb.__version__
'1.2.2'