Some assert methods can be updated

[jian.song]

From python 2.7 onwards, some new method such as assertIsNone
equivalent to the assertEqual,this will simplify the number of
parameters.

refer to [1] for more information

[1]:https://docs.python.org/2.7/library/unittest.html#unittest.TestCase.assertIsNone

[Zhao Chao (zhaochao1984)]

This should be fixed after this patch merge:
https://review.openstack.org/#/c/364375/