Follow-up from "Fix lint issues": Avoid the need to disable `assignment-from-no-return` for abstract methods

[See original issue on GitLab](https://gitlab.com/BuildStream/buildstream/-/issues/724)
In GitLab by [[Gitlab user @juergbi]](https://gitlab.com/juergbi) on Oct 24, 2018, 16:10

The following discussion from !892 should be addressed:

- [ ] [[Gitlab user @juergbi]](https://gitlab.com/juergbi) started a [discussion](https://gitlab.com/BuildStream/buildstream/merge_requests/892#note_111482557): (+3 comments)

> > We can probably get rid of the handful of `# pylint: disable=assignment-from-no-return` by using [[Gitlab user @abc]](https://gitlab.com/abc) around the code base. Looking at how many of those exceptions we need, this might well be worthwhile. Definitely a new MR/issue, but still worth noting.
>
> I don't like requiring `disable=assignment-from-no-return` for this common pattern. If `[[Gitlab user @abc]](https://gitlab.com/abc)` indeed works for this, shouldn't this be a rather simple improvement and better done as part of this MR?

Start with the linked GitLab issue and merge-request discussion, then locate the abstract methods that require assignment-from-no-return disables. Review whether the proposed abc approach applies across the codebase; done means the relevant disables can be removed while linting still passes.

Written by the indexing model from the issue text.