Block flavor creation until main database is empty

This makes Flavor.create() fail until the main database has had all
of its flavors migrated. Since we want to avoid any overlap or clashes
in integer ids we need to enforce this. The flavor API was poorly
designed in that it exposes this internal id. Luckily, flavor creation
is infrequent and flavor migration is fast.

The flavors in our database are hard-coded in the first migration,
which means we have to basically do the migration during every
unit test in order to avoid having a legacy environment. Since that
leaves us with deleted flavors in the DB (which screws up the DB
archiving tests), this adds a hard_delete flag to the migration to
do an actual purge of those from our database. What a mess.

Related to blueprint flavor-cell-api

Depends-On: I8ab03af9d2f4974f26a7f8487ec978caea957e45
Change-Id: Iea063448f43da1043d16dd521d255dd29a0e1bc5

nova/test.py

@@ -49,6 +49,7 @@ from nova import db
 from nova.network import manager as network_manager
 from nova.network.security_group import openstack_driver
 from nova.objects import base as objects_base
+from nova.objects import flavor as flavor_obj
 from nova.tests import fixtures as nova_fixtures
 from nova.tests.unit import conf_fixture
 from nova.tests.unit import policy_fixture
@@ -213,6 +214,11 @@ class TestCase(testtools.TestCase):
         if self.USES_DB:
             self.useFixture(nova_fixtures.Database())
             self.useFixture(nova_fixtures.Database(database='api'))
+            # NOTE(danms): Flavors are encoded in our original migration
+            # which means we have no real option other than to migrate them
+            # onlineish every time we build a new database (for now).
+            ctxt = context.get_admin_context()
+            flavor_obj.migrate_flavors(ctxt, 100, hard_delete=True)
         elif not self.USES_DB_SELF:
             self.useFixture(nova_fixtures.DatabasePoisonFixture())