Add a quiet option to CLI commands

Addresses https://trac.openmicroscopy.org.uk/ome/ticket/12291. Closes #2476.

This PR:
- adds an extra `isquiet` attribute `omero.cli.Context` to disable `self.ctx.err` printing to `sys.stderr` 
- exposes a `-q` flag across all commands requring a connection, i.e. using all CLI commands which parser calls `add_login_arguments`
- as a consequence of the latter, MODIFIES the behavior of `bin/omero hql -q` which now silences `self.ctx.err()`. Note `bin/omero hql --quiet` is still behaving as previously.
- adds  an integration test for the diagnostics output of `bin/omero login`


Can we go for the simpler change here?