OpenStack now has dropped support for python 2.6 and lower.
So we don't need to define an assertDictEqual() for python
lower than 2.7.
Further, assertEqual() in testtools is able to handle dicts
comparation, just the same as assertDictEqual() in unittest2.
So we do't need to call assertDictEqual() for dicts any more.
Change-Id: I114bd434f9137844c25f0824be9b6ddee28ce7ee