Multi-backend domain code/tests could use a bit of tidy up

[Henry Nash]

The multi-domain backend code has a number of tidy-up items that were deferred from the review:

- Re-factoring _set_domain_id_and_mapping() in identity/core.py
- Potential relaxation of the constraint that user/group membership cannot cross a backend boundary
- Corner case testing for exceptions
- Potentially add anything multi-backend test that is in-between the simple and complex tests that have already been defined (e.g. add one that as SQL as the default identity backend, with one LDAP specific domain)
- Potentially add a test that puts the SQL driver as a specific backend driver for a domain (since we only support one SQL driver, this is an odd configuration, but still probably worth while)

[Henry Nash (henry-nash)]

The last item listed:

- Potentially add a test that puts the SQL driver as a specific backend driver for a domain (since we only support one SQL driver, this is an odd configuration, but still probably worth while)

has been fixed as part of: https://review.openstack.org/#/c/121246/

[Steve Martinelli (stevemar)]

wondering if this is still an issue?

[Steve Martinelli (stevemar)]

AFAICT this has been fixed