MAR-22: Implemented tests for the common role:

- Added missing documentation for pipreqcheck_uid and pipreqcheck_gid
parameters.
- Use static-hashed passwords for reproducibility during testing in test
playbook.
- Install Emacs and libmariadb-client-lgpl-dev-compat via test playbook on one
of the testing instances in order to test related tasks.
- Fixed parameter for connection limitting in test playbook.
- Added explicit parameters to test playbook for pipreqcheck_gid and
pipreqcheck_uid.
- Fixed deployment of ferm configuration file ot include setting user/group and
mode.
- Added tests covering common deployment, deployment when only mandatory
parameters are provided, and deployment when optional parameters are set as
well.