PYTHON-1906 Skip new SRV test if dnspython isn't available

Author: behackett

test/test_dns.py

@@ -108,6 +108,7 @@ def create_tests():
 
 class TestParsingErrors(unittest.TestCase):
 
+ @unittest.skipUnless(_HAVE_DNSPYTHON, "DNS tests require the dnspython module")
  def test_invalid_host(self):
  self.assertRaisesRegex(
  ConfigurationError,