Add paste to the default list of loggers in tests

We have a list of some external things we mostly silence by default. It
currently does not include paste, so we get a lovely:

 No handlers could be found for logger "paste.httpserver.ThreadPool"

Add paste to the list and make the noise go away.

Change-Id: I1eae75e18b01c57c632c76c49e59642871583328
diff --git a/tests/base.py b/tests/base.py
index 77c0644..faf3268 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -1555,7 +1555,7 @@
         # from libraries that zuul depends on such as gear.
         log_defaults_from_env = os.environ.get(
             'OS_LOG_DEFAULTS',
-            'git.cmd=INFO,kazoo.client=WARNING,gear=INFO')
+            'git.cmd=INFO,kazoo.client=WARNING,gear=INFO,paste=INFO')
 
         if log_defaults_from_env:
             for default in log_defaults_from_env.split(','):