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: I870286a2557e41099597c22dc9747743e1077615
bf0dc265ae