Log python warnings only once to limit size of CI jobs' output

This patch sets to log python warnings only once in the tests and also
sets some of the oslo_context warnings, related to the policy
enforcement to be ignored to limit size of the output of e.g. unit tests
jobs.

Change-Id: I28d8a193198bbc4249cf7a37d70f065efd908c41

neutron/tests/base.py

@@ -26,6 +26,7 @@ import os.path
 import queue
 import threading
 from unittest import mock
+import warnings
 
 import eventlet.timeout
 import fixtures
@@ -226,6 +227,17 @@ class DietTestCase(base.BaseTestCase, metaclass=_CatchTimeoutMetaclass):
     def setUp(self):
         super(DietTestCase, self).setUp()
 
+        # NOTE(slaweq): Make deprecation warnings only happen once.
+        warnings.simplefilter("once", DeprecationWarning)
+
+        # NOTE(slaweq): Let's not display such warnings in tests as we know
+        # that we have many places where policy enforcement depends on values
+        # like is_admin or project_id and there can be a lot of such warnings
+        # in the logs
+        warnings.filterwarnings(
+            'ignore', message=(
+                'Policy enforcement is depending on the value of '))
+
         # Suppress some log messages during test runs, otherwise it may cause
         # issues with subunit parser when running on Python 3. It happened for
         # example for neutron-functional tests.