Use dict.keys() for key iteratation

1.As mentioned in [1], we should avoid usingg
six.iteritems to achieve iterators. We can
use dict.items instead, as it will return
iterators in PY3 as well. And dict.items/keys
will more readable. 2.In py2, the performance
about list should be negligible, see the link [2].
[1] https://wiki.openstack.org/wiki/Python3
[2] http://lists.openstack.org/pipermail/openstack-dev/2015-June/066391.html

Change-Id: If262e92b06e6cdef7429bd55549435c98e39c603

zaqar/transport/middleware/profile.py

@@ -13,7 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import six
 import six.moves.urllib.parse as urlparse
 import webob
 
@@ -78,7 +77,7 @@ class ProfileWSGIMiddleware(object):
     def _trace_is_valid(self, trace_info):
         if not isinstance(trace_info, dict):
             return False
-        trace_keys = set(six.iterkeys(trace_info))
+        trace_keys = set(trace_info.keys())
         if not all(k in trace_keys for k in web._REQUIRED_KEYS):
             return False
         if trace_keys.difference(web._REQUIRED_KEYS + web._OPTIONAL_KEYS):