CLI fs plugin: integration tests and bug fixes

Fixes https://trac.openmicroscopy.org.uk/ome/ticket/12330

This PR addresses most of the bugs reported in the ticket above:
- `bin/omero fs sets --with-transfer MODE1 [MODE2]` should now properly filter all transfer modes
- `bin/omero fs sets --check` should fail fast when logging in as a non-admin
- `bin/omero fs sets --with-transfer` is not allowed
- Integration tests have been added and should be verified to be passing on the corresponding CI job
- Additionally an `error_admin_only()` method has been added to `cli.py` and used in `ldap.py` /cc @bpindelski