Force mistral tests to log in mistral.log

Let mistral unit tests worker log in mistral.log instead of stderr and
stdout.
This way, unit tests results are much more easier to read and review.

Change-Id: I469ff43f6e986502c48a98a664c9a4a6532b633c
Signed-off-by: Arnaud M <arnaud.morin@gmail.com>

mistral/tests/unit/base.py

@@ -33,10 +33,14 @@ from mistral.services import security
 from mistral.tests.unit import config as test_config
 from mistral import version
 
-RESOURCES_PATH = 'tests/resources/'
+CONF = cfg.CONF
+
+logging.register_options(CONF)
+CONF.set_override('log_file', 'mistral.log')
+logging.setup(CONF, 'mistral')
 LOG = logging.getLogger(__name__)
 
-
+RESOURCES_PATH = 'tests/resources/'
 test_config.parse_args()