Fix sqlalchemy operational error

This is a workaround for the following error.

Traceback (most recent call last):
  File "/opt/stack/quantum/bin/quantum-server", line 24, in <module>
    server()
  File "/opt/stack/quantum/quantum/server/__init__.py", line 58, in main
    args=args)
  File "/opt/stack/quantum/quantum/service.py", line 98, in serve_wsgi
    service.start()
  File "/opt/stack/quantum/quantum/service.py", line 43, in start
    self.wsgi_app = _run_wsgi(self.app_name, self.conf, self.conf_file)
  File "/opt/stack/quantum/quantum/service.py", line 107, in _run_wsgi
    None)
  File "/opt/stack/python-quantumclient/quantum/common/config.py", line 319, in load_paste_app
    app = deploy.loadapp("config:%s" % conf_file, name=app_name)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 247, in loadapp
    return loadobj(APP, uri, name=name, **kw)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 272, in loadobj
    return context.create()
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 710, in create
    return self.object_type.invoke(self)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 144, in invoke
    **context.local_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/util.py", line 56, in fix_call
    val = callable(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/paste/urlmap.py", line 25, in urlmap_factory
    app = loader.get_app(app_name, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 350, in get_app
    name=name, global_conf=global_conf).create()
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 710, in create
    return self.object_type.invoke(self)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 203, in invoke
    app = context.app_context.create()
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 710, in create
    return self.object_type.invoke(self)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 146, in invoke
    return fix_call(context.object, context.global_conf, **context.local_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/util.py", line 56, in fix_call
    val = callable(*args, **kw)
  File "/opt/stack/quantum/quantum/wsgi.py", line 639, in factory
    return cls()
  File "/opt/stack/quantum/quantum/api/__init__.py", line 46, in __init__
    self._setup_routes(mapper, options)
  File "/opt/stack/quantum/quantum/api/__init__.py", line 53, in _setup_routes
    self._setup_base_routes(mapper, options, self._version)
  File "/opt/stack/quantum/quantum/api/__init__.py", line 60, in _setup_base_routes
    plugin = manager.QuantumManager.get_plugin(options)
  File "/opt/stack/quantum/quantum/manager.py", line 87, in get_plugin
    cls._instance = cls(options, config_file)
  File "/opt/stack/quantum/quantum/manager.py", line 82, in __init__
    self.plugin = plugin_klass()
  File "/opt/stack/quantum/quantum/plugins/ryu/ryu_quantum_plugin.py", line 119, in __init__
    super(RyuQuantumPlugin, self).__init__(CONF_FILE, __file__, configfile)
  File "/opt/stack/quantum/quantum/plugins/ryu/ovs_quantum_plugin_base.py", line 78, in __init__
    db.configure_db(options)
  File "/opt/stack/quantum/quantum/db/api.py", line 78, in configure_db
    register_models()
  File "/opt/stack/quantum/quantum/db/api.py", line 103, in register_models
    BASE.metadata.create_all(_ENGINE)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/schema.py", line 2515, in create_all
    tables=tables)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 2234, in _run_visitor
    conn._run_visitor(visitorcallable, element, **kwargs)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1904, in _run_visitor
    **kwargs).traverse_single(element)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/sql/visitors.py", line 86, in traverse_single
    return meth(obj, **kw)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/ddl.py", line 67, in visit_metadata
    self.traverse_single(table, create_ok=True)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/sql/visitors.py", line 86, in traverse_single
    return meth(obj, **kw)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/ddl.py", line 86, in visit_table
    self.connection.execute(schema.CreateTable(table))
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1405, in execute
    params)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1496, in _execute_ddl
    compiled
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1646, in _execute_context
    context)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1639, in _execute_context
    context)
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 330, in do_execute
    cursor.execute(statement, parameters)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 174, in execute
    self.errorhandler(self, exc, value)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
sqlalchemy.exc.OperationalError: (OperationalError) (1075, 'Incorrect table definition; there can be only one auto column and it must be defined as a key') '\nCREATE TABLE tunnel_key (\n\tnetwork_id VARCHAR(255) NOT NULL, \n\ttunnel_key INTEGER NOT NULL AUTO_INCREMENT, \n\tPRIMARY KEY (network_id, tunnel_key)\n)\n\n' ()