Related to this one: #8285

Looks like my previous review failed to identify a number of issues and possible improvements. Sorry about that. I was focused into the changes to Build side, not how it's configured.

My further comments:

• Please use snake_case for new code.

• Steps have doStepIf. I think our property could be named do_build_if to keep consistency.

• BuildFactories currently behave essentially as a list of build steps now. The configuration lives in a BuilderConfig. I think it makes sense to move do_build_if there as well. The the line self.skipBuild = self.skipBuildIf(self) would become self.do_build = self.builder.config.do_build_if(self) or similar.

• There won't be need for setSkipBuildIf anymore? A static configuration will be enough, won't it?

• Integration test is missing. Easiest would be to add one to master/buildbot/test/integration/test_custom_buildstep.py. Add builder_kwargs argument to create_config_for_step and maybe use this test as a base for your test:

    @defer.inlineCallbacks
    def test_step_raising_buildstepfailed_in_start(self):
        builder_id = yield self.create_config_for_step(FailingCustomStep())

        yield self.do_test_build(builder_id)
        yield self.assertBuildResults(1, results.FAILURE)