DB migration 57 failed on db2

[Ethan Lynn]

My db backend is db2, and db_sync failed at 057.
[root@dn1-n6 ~]# heat-manage db_sync
ERROR: list index out of range
[root@dn1-n6 ~]# heat-manage db_version
56

Error code is:
https://github.com/openstack/heat/blob/master/heat/db/sqlalchemy/migrate_repo/versions/057_resource_uuid_to_id.py#L41-L44
    fkc_name = inspector.get_foreign_keys('resource_data')[0]['name']
    fkc = ForeignKeyConstraint([rd_table.c.resource_id], [res_table.c.id],
                               fkc_name)
    migrate_engine.execute(DropConstraint(fkc))

get_foreign_keys returns [] in db2.

[Ethan Lynn (ethanlynn)]

This issue block our internal build.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/163748

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/163748
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=d005f2db6c47ff546c7ac173724fc5f3ee4e37cb
Submitter: Jenkins
Branch: master

commit d005f2db6c47ff546c7ac173724fc5f3ee4e37cb
Author: Ethan Lynn <email address hidden>
Date: Thu Mar 12 18:05:30 2015 +0800

    Fix db migration script 057 failure on db2

    Add a if condition before drop foreign key constraint.

    Closes-Bug: #1431250
    Change-Id: Idc3afeb8739a608ae618c605eb730a4eb3e3da84