Switch from unittest2 compat methods to Python 3.x methods
Switch from unittest2 compat methods to Python 3.x methods

With the removal of Python 2.x we can remove the unittest2 compat
wrappers and switch to assertCountEqual instead of assertItemsEqual

We have been able to use them since then, because
testtools required unittest2, which still included it. With testtools
removing Python 2.7 support [3][4], we will lose support for
assertItemsEqual, so we should switch to use assertCountEqual.

[1] - https://bugs.python.org/issue17866
[2] - https://hg.python.org/cpython/rev/d9921cb6e3cd
[3] - testing-cabal/testtools#286
[4] - testing-cabal/testtools#277^

Change-Id: I5e02a7ed7803e21ad2baa93fccd00a23cda3da79

openstack/python-barbicanclient