test_migration needs some refactor due to oslo.db 1.1.0 release

[Ann Taraday]

test_migration contains some methods like overriding compare_server_default and compare_foreign_keys that was added directly in ModelsMigrationsSync class in oslo.db only in 1.1.0.

Also as now migrations refactoring is fully finished, there is no need to have separate classes for each plugin.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/135188

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/135188
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=fd0417d000b0e8f0ff52b5f0d7ca9eb4029071a3
Submitter: Jenkins
Branch: master

commit fd0417d000b0e8f0ff52b5f0d7ca9eb4029071a3
Author: Ann Kamyshnikova <email address hidden>
Date: Tue Nov 18 11:01:35 2014 +0300

    Refactor test_migration

    test_migration contains some methods like overriding compare_server_default
    and compare_foreign_keys that was added directly in ModelsMigrationsSync
    class in oslo.db only in 1.1.0.

    Also as now migrations refactoring is fully finished, there is no
    need to have separate classes for each plugin.

    Closes-bug: #1393691

    Change-Id: I65b40fe52c2c6f4bae88e125bd1ee501aaa24114