IntegrityError running sql tests on MySQL/Postgres

When running tests/test_sql_upgrade.py against a MySQL or Postgres database the tests fail with an IntegrityError.

see: http://paste.openstack.org/show/36045/

It appears that this is because migration 020 imposes a foreign key restraint in downgrade that wasn't initially present.

Printing the table structure of 'metadata' before migration 020 gives:

Table('metadata', MetaData(bind=Engine(mysql://root:test@localhost/keystonetest?charset=utf8)),
Column(u'user_id', VARCHAR(length=64), table=<metadata>, primary_key=True, nullable=False),
Column(u'tenant_id', VARCHAR(length=64), table=<metadata>, primary_key=True, nullable=False),
Column(u'data', MEDIUMTEXT(), table=<metadata>), schema=None)

Printing the table structure of 'metadata' after migration 020 downgrade gives:

Table('metadata', MetaData(bind=Engine(mysql://root:test@localhost/keystonetest?charset=utf8)),
Column('user_id', String(length=64), ForeignKey('user.id'), table=<metadata>, primary_key=True, nullable=False),
Column('tenant_id', String(length=64), table=<metadata>, primary_key=True, nullable=False),
Column('data', Text(), table=<metadata>), schema=None)

This is not relevant to whether user_id should be a foreign key, simply that the downgrade does not match the upgrade.