Fix build_success vs. artifacts dependency problem

The build success links are symbolic files that are addressed to solve the problem where we overwrite statefiles and logs. The build success link is read before creating workitem and if it is found, the workitem will be saved in done state. This will avoid creating workitempaths for workitems that have already been done.

However, the build success links are cache files and they introduce problems some times artifacts are missing from storage and there is no clear indications why this is. There are at least to solutions to this problem:

Large effort) Remove build success links and verify Done state by parsing thrift files

    Requires large refactoring of storage code

Small effort) Remove build_success link if artifacts are missing

    Commit: https://codereview.qt-project.org/#/c/205578 (abandoned)