Add missing log_format definition

As part of shrinking the base test class file down to just the core
functionality the definition for the logging fixture log format was
accidently removed. This causes any test based on the test class to
fail during setUp. This commit fixes the oversight by adding it back.

tempest_lib/base.py

@@ -52,6 +52,12 @@ def validate_tearDownClass():
 class BaseTestCase(BaseDeps):
     setUpClassCalled = False
 
+    # NOTE(sdague): log_format is defined inline here instead of using the oslo
+    # default because going through the config path recouples config to the
+    # stress tests too early, and depending on testr order will fail unit tests
+    log_format = ('%(asctime)s %(process)d %(levelname)-8s '
+                  '[%(name)s] %(message)s')
+
     @classmethod
     def setUpClass(cls):
         if hasattr(super(BaseTestCase, cls), 'setUpClass'):