Fix py34 issues

The Nova project now has clean tox py34 runs with a limited set
of the UT.  This change set fixes two existing py34 issues
and allows py34 to run cleanly. The fixed issues are:

 - Use the 'builtins' module instead of __builtin__.
 - Don't log exceptions before they are raised.

Change-Id: Ib66e36c54353833b8ec35ff6f34b3cd81d609334

nova_powervm/tests/virt/powervm/test_image.py

@@ -15,16 +15,22 @@
 #    under the License.
 
 import mock
+import six
 
 from nova import test
 
 from nova_powervm.virt.powervm import image
 
+if six.PY2:
+    _BUILTIN = '__builtin__'
+else:
+    _BUILTIN = 'builtins'
+
 
 class TestImage(test.TestCase):
 
     @mock.patch('nova.utils.temporary_chown')
-    @mock.patch('__builtin__.open')
+    @mock.patch(_BUILTIN + '.open')
     @mock.patch('nova.image.api.API')
     def test_stream_blockdev_to_glance(self, mock_api, mock_open, mock_chown):
         mock_open.return_value.__enter__.return_value = 'mock_stream'

nova_powervm/virt/powervm/vm.py

@@ -267,7 +267,6 @@ class VMBuilder(object):
         # Check if this is a valid attribute
         if key not in self._ATTRS_MAP.keys():
             exc = exception.InvalidAttribute(attr=key)
-            LOG.exception(exc)
             raise exc
 
         return True