P8: Fix pep8 error in cyborg/tests and add post_mortem_debug.py

1. Add post_mortem_debug.py because accelerator/drivers/gpu/test_base.py
lack this file[1]. Reference Neutron[2,3].

[1]. https://github.com/openstack/cyborg/blob/master/cyborg/tests/base.py#L104
[2]. 43352e67e5/neutron/tests/base.py (L229)
[3]. https://github.com/openstack/neutron/blob/master/neutron/tests/post_mortem_debug.py

2. Remove old useless file cyborg/tests/unit/fake_accelerator.py[4,5].

[4]. https://github.com/openstack/cyborg/search?q=fake_accelerator_obj&unscoped_q=fake_accelerator_obj
[5]. https://review.opendev.org/#/c/625630/

Change-Id: I147bfe9a8dfb6bdbe7e59fa3dc0c146c70e4d3a7

cyborg/tests/unit/api/controllers/v2/test_device_profiles.py

@@ -18,8 +18,6 @@ from six.moves import http_client
 
 from oslo_serialization import jsonutils
 
-from cyborg.api.controllers.v2.device_profiles import DeviceProfilesController
-from cyborg.common import exception
 from cyborg.tests.unit.api.controllers.v2 import base as v2_test
 from cyborg.tests.unit import fake_device_profile
 
@@ -68,7 +66,8 @@ class TestDeviceProfileController(v2_test.APITestV2):
         data = self.get_json(self.DP_URL, headers=self.headers)
         out_dps = data['device_profiles']
 
-        self.assertTrue(isinstance(out_dps, list))
+        result = isinstance(out_dps, list)
+        self.assertTrue(result)
         self.assertTrue(len(out_dps), len(self.fake_dp_objs))
         for in_dp, out_dp in zip(self.fake_dp_objs, out_dps):
             self._validate_dp(in_dp, out_dp)