workflows: hotfix unittest

* Improves tests stability.

* Simplifies workflow engine.

* Fixes the endlessy working workflow engine bug.

* Reduces log produces by workflows unit tests.

* Inverts arguments in test to expected val, current val.

Signed-off-by: Guillaume Lastecoueres <guillaume.lastecoueres@cern.ch>
Co-authored-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Reported-by: Yoan Blanc <yoan.blanc@cern.ch>
Tested-by: Yoan Blanc <yoan.blanc@cern.ch>
tags: REST API and testing

* Creates API for tags, in order to have a reusable API
  both for restful API and views probably.

* Refactors tags REST API in order to use the new tag API.

* Tests the tags REST API.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>