fix: TCs that should expect a 405 instead of a 400

See merge request !116

Refactoring to analyse all the checks and review the operation to be controlled in the analysis of the TS

fix: expect a 204 when updates are ignored in update or append attributes operations

See merge request !115

- calling Suite Teardown only cleans up data from last TC in the suite
- clearly identify setups steps in TCs
- prefer Set Test Variable when variable is set in a TC

- was the same as Delete Entity by Id keyword

- moreover, it was not deleted, which broke some subscriptions tests later