This commit add the possibility to add custom checks to python steps,
as well as ignoring triggered result if log of level error/warning
is not considered as a problem.
A lot of things have to be mocked during runbot tests, as a consequence,
a lot of patch decorators accumulate in a big stack uppon some tests
methods.
Also, a lot of mocks are used multiple times among tests.
With this commit, a new RunbotClass is added that comes with patches
ready to be started. A start_patcher helper method is available to start
a patch and add the appropriate stop in a cleanup.
Also, when a build is created in the tests, the _get_params method is
always called, resulting in an annoying git warning.
With this commit, a create_build method is added on the test class, that
way the _get_params is always mocked when a build is created.
