Convert SessionControl._parse_conn into a static method
Add unit tests for static SessionsControl._parse_conn() method
Use group naming for clarity in _parse_conn and add docstring
Extend unit tests to cover empty string input
Add tests for connection string parsing with wild users and bad ports

- Increase stringency of regular expression to match up to 5 digits for ports
- Test connection string with user containing both : and @ characters
- Add test with invalid port and check the port is parsed with the server name
Merge pull request #2388 from sbesson/rebased/develop/parse_conn_tests

Add unit tests for CLI connection string parser (rebased onto develop)