Downgrade of assignment to grant tables has issues with postgresql & mysql

[Henry Nash]

There are two issues:

1) The downgrade on Mysql may fail due to not committing changes at the appropriate time when there are multiple assignment entries being mapped back into a single grant entry. This works fine with postgresql (appears to an sqlalchemy issue)

2) test_sql_upgrade fails to close an outer session that has done a SELECT on the grant tables we want to drop - which will cause the drop to block on databases other the sqllite. This doesn't affect a production migration, but stops the tests.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/76341

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/76341
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=4d505e63902bd31e40904a0c9045b9b07d5bdb5a
Submitter: Jenkins
Branch: master

commit 4d505e63902bd31e40904a0c9045b9b07d5bdb5a
Author: Henry Nash <email address hidden>
Date: Tue Feb 25 17:51:43 2014 +0000

    Fix issue with DB upgrade to assignment table

    There are two changes:
    - Commit changes to the grant tables after each update to ensure MySQL
      doesn't get confused when there are multiple assignments for a given
      actor/target (Postgresql doesn't have this issue)
    - Close any sessions in test_sql_upgarde before we call the migrations,
      to ensure table dropping won't be blocked

    Fixes bug 1284700

    Change-Id: I81704b17ea9c11be926018df125fcfdb79ee6271