Python 3: use dict.values instead of dict.itervalues

This works with both Python 2 and 3, and should not have any performance
impact.

Change-Id: I2a14945c60de513b91c6f022ff5dcc503ce2a8ad
Blueprint: neutron-python3
diff --git a/neutron/tests/tempest/common/isolated_creds.py b/neutron/tests/tempest/common/isolated_creds.py
index b4de93b..5da24a9 100644
--- a/neutron/tests/tempest/common/isolated_creds.py
+++ b/neutron/tests/tempest/common/isolated_creds.py
@@ -369,7 +369,7 @@
         if not self.isolated_creds:
             return
         self._clear_isolated_net_resources()
-        for creds in self.isolated_creds.itervalues():
+        for creds in self.isolated_creds.values():
             try:
                 self._delete_user(creds.user_id)
             except lib_exc.NotFound: