Revert "Only call create_all once"

Since this database is in memory there seems to be an interaction with
tox and how it sets up and runs tests. So let's just create it each time

This reverts commit b32284e787.

Change-Id: I56be0354eae2028f50efe6d5e8034dcdb1766b54

neutron_classifier/tests/test_db_api.py

@@ -19,7 +19,6 @@ from sqlalchemy.orm import sessionmaker
 from oslo_utils import uuidutils
 from oslotest import base
 
-CREATED = False
 
 FAKE_SG_RULE = {'direction': 'INGRESS', 'protocol': 'tcp', 'ethertype': 'IPv6',
                 'tenant_id': 'fake_tenant', 'port_range_min': 80,
@@ -47,11 +46,7 @@ class DbApiTestCase(base.BaseTestCase):
     def setUp(self):
         super(DbApiTestCase, self).setUp()
         self.context = ClassifierTestContext()
-
-        if not CREATED:
-            models.Base.metadata.create_all(self.context.engine)
-            global CREATED
-            CREATED = True
+        models.Base.metadata.create_all(self.context.engine)
 
     def _create_classifier_group(self, service):
         cg = models.ClassifierGroup()