test that configuration may be influenced via the designed-in environment variables.

For example, make sure that 
```
$ export PYTHON_IRODSCLIENT_CONFIG__GENQUERY1__IRODS_QUERY_LIMIT=128
$ python -ic 'import irods.query; print (irods.query.IRODS_QUERY_LIMIT ==
    irods.client_configuration.genquery1.irods_query_limit ==
    128)'
```
produces an output of `True`.

Only, it might be advisable to make the tests even more general than that.


