Remove graduated test and fixtures libraries

The config fixture is now part of oslo.config and the other ones are
part of oslotest. Let's remove them!

Change-Id: I90ab87772bda17a3f7872c41db869c4e278cf57c
Clean requirements

It seems that we removed a lot of code lately but we forgot to clean the
requirements files accordingly.

Change-Id: Ifa9d1fa0cb5d39c8fc7aad35a757d34fb6108bbe
Stop testing notifier under python 3

Change-Id: I6aee37f0f2cef75bafb8ed35cdb82ca203bd32cc
Merge "Remove graduated test and fixtures libraries"
Merge "Clean requirements"
Merge "Stop testing notifier under python 3"