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`


This is likely the only line that makes me semi-nervous, not knowing how all other plugins are using `self.ctx.err`:
```
components/tools/OmeroPy/src/omero/plugins$ git grep "ctx.err" | cut -f1 -d: | uniq -c
     14 admin.py
      1 basics.py
      3 cecog.py
      3 db.py
      2 export.py
      4 ldap.py
      1 obj.py
      3 prefs.py
     10 script.py
      8 sessions.py
      7 tag.py
      2 user.py
      4 web.py
components/tools/OmeroPy/src/omero/plugins$ git grep "ctx.err" | wc -l
62

```