tenant dictionary passed to (SQL)Identity.create_tenant is modified

The Tenant.to_dict method of the SQL backend adds an 'extra' key in the tenant dictionary that was passed to create_tenant.

This is apparent only when running the SQL tests before the LDAP ones:

nosetests -s tests/test_backend_sql.py:SqlIdentity.test_authenticate tests/test_backend_ldap.py:LDAPIdentity.test_authenticate

======================================================================
FAIL: test_authenticate (test_backend_ldap.LDAPIdentity)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/lib/openstack-keystone-test/tests/test_backend.py", line 67, in test_authenticate
    self.assertDictEquals(tenant_ref, self.tenant_bar)
  File "/var/lib/openstack-keystone-test/keystone/test.py", line 305, in assertDictEquals
    'Expected key %s not in %s.' % (k, actual))
AssertionError: Expected key extra not in {'id': 'bar', 'name': 'BAR'}.
-------------------- >> begin captured logging << --------------------
~~ snipped lots of LDAP logs ~~

Running them in the usual alphabetic order, doesn't show any errors (nosetests -s tests/test_backend_ldap.py:LDAPIdentity.test_authenticate tests/test_backend_sql.py:SqlIdentity.test_authenticate)

The simple fix is to pass a copy of the tenant fixture to create_tenant in the load_fixtures function. OTOH is this really the proper functionality for the Identity backend? i.e. modifying the dictionary passed in to create_tenant?

The fix is trivial for both cases, so I'd just like a second opinion on where to fix it: keystone.test vs keystone.identity.backends.sql