Add cloudinit.tests.util for shared testing code.

Starting with keeping the try/except to find mock on both Python 2 and
Python 3 in one place.

Change-Id: I4fa5e6e3f6610f6eb2601d4c3cb51d76565dd3c0

cloudinit/tests/osys/test_base.py

@@ -15,12 +15,8 @@
 
 import unittest
 
-try:
-    import unittest.mock as mock
-except ImportError:
-    import mock
-
 from cloudinit.osys import base
+from cloudinit.tests.util import mock
 
 
 class TestOSUtils(unittest.TestCase):

cloudinit/tests/util.py

@@ -0,0 +1,4 @@
+try:
+    from unittest import mock
+except ImportError:
+    import mock  # noqa