Add CLI multi tenancy tests

- Refactor CLI tests infrastructure
- Added auth in Mistral by two different users
- Removed tearDown methods, add usage of addCleanup methods
- Create new base methods like 'workbook-create', which contain
addCleanup call and makes tests more clear for reading

Implements: blueprint mistral-milti-tenancy-tests

Change-Id: I4a58b4c1bfff192912f3f1d149869656f7e9c54b