Fix foreign key drop and recreation

[Octave Orgeron]

There are two migration scripts in Keystone that make table changes without dropping and recreating foreign key constraints. This causes problems with portability with other MySQL database types, in particular MySQL Cluster (NDB), which requires strict adherence to ACID model. The two scripts are:

012_contract_add_domain_id_to_idp.py
015_contract_update_federated_user_domain.py

This fix follows the methods already in use in Keystone for properly handling the dropping and recreation of foreign keys around table changes which are in:

014_contract_add_domain_id_to_user_table.py
092_make_implied_roles_fks_cascaded.py

This fix adds the get_fk_name to the upgrades module, making it available across Keystone. The plan is to eventually add this function to oslo.db and make it available across OpenStack to help with these operations.

[Steve Martinelli (stevemar)]

Thanks for the initial diagnosis Octave!

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/431229

[Lance Bragstad (lbragstad)]

Automatically unassigning due to inactivity.

[Lance Bragstad (lbragstad)]

Reassigning since this is being worked in review and generating a lot of discussion.

[Lance Bragstad (lbragstad)]

Automatically unassigning due to inactivity.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Gage Hugo <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/keystone/+/431229
Reason: Abandoning since there hasn't been any recent activity, if anyone wants to continue this work, please feel free to restore this or create a new change.