Checking specific mistakes can be automated via hacking rules.
This patch:
* adds HACKING.rst - list of rules;
* adds rally.hacking - module for implementation of rules;
* edits tox.ini, so hacking rules will be checked during pep8 test;
* adds 3 rules related to mistakes in `assert_*` methods from `mock`
library. Also tests, which are failed due to these rules, are fixed.
Closes-Bug: #1305991
Change-Id: I605dd5cfba4eb83d0735e4f9f3ab4e44e149d041
2de00e070b