Fix test_shadow_tables() on PostgreSQL/MySQL

Migration 209 creates a few new tables for storing of temporary
data (they all have names starting with 'dump_'). This breaks
test_shadow_tables() of ArchiveTestCase, which checks that every
existing table has a corresponding shadow table.

The DB API tests currently succeed only because they are run on
SQLite, and migration 209 is no-op for SQLite DB backend.

Blueprint: db-api-tests-on-all-backends

Change-Id: I632454fdacf35be972668f394496466978b5616f
Fix FK violation errors in InstanceActionTestCase

A few tests of InstanceActionTestCase inserts rows,
that have no corresponding values in 'instances' table,
and this causes FK violation errors.

This change fixes InstanceActionTestCase when running
tests on PostgreSQL/MySQL or on SQLite with FKs enabled.

Blueprint: db-api-tests-on-all-backends

Change-Id: I9ec39d5f4c21ba5a627b289164480c694bc1539c
Merge "Fix test_shadow_tables() on PostgreSQL/MySQL"
Merge "Fix FK violation errors in InstanceActionTestCase"