added SkipTest for cname tests if dnspython is not installed

test/unit/common/middleware/test_cname_lookup.py

@@ -14,11 +14,16 @@
 # limitations under the License.
 
 import unittest
+from nose import SkipTest
 
 from webob import Request
 
+try:
+    # this test requires the dnspython package to be installed
     from swift.common.middleware import cname_lookup
-
+    skip = False
+except ImportError:
+    skip = True
 
 class FakeApp(object):
 
@@ -33,6 +38,8 @@ def start_response(*args):
 class TestCNAMELookup(unittest.TestCase):
 
     def setUp(self):
+        if skip:
+            raise SkipTest
         self.app = cname_lookup.CNAMELookupMiddleware(FakeApp(),
                                                       {'lookup_depth': 2})