tests: update after removing of redundant amend commit
Following e8a7c1a0565a, temporary amend commits has been removed impacting all
revision numbers in tests including amend operations.
Update tests case to use description or hashes when possible and update
revisions number when not.
topic: setup 'topic' value for working ctx
The way amend work in core change in e8a7c1a0565a. The intermediate commit
disappear and we can no longer rely on it to carry the topic value to amend. To
fix this, we ensure the current topic value can be retrieved through the
`workingctx.extra()` value. Since there is no way to carry a "missing" key
information in a way that survives and "dict.update" call. We also has to
introduce hacking behavior about a special empty value for topic.