Make sure we set the error message in the json as defined in the test

jail2ban/__init__.py

@@ -88,6 +88,9 @@ def create_app():
         name = untaint(PAT_NAME, name)
         app.logger.info(f'Flushing table f2b-{name}'
                         f' in anchor f2b-jail/{remote_user}')
+        reply = {'anchor': f'f2b-jail/{remote_user}',
+                        'table': f'f2b-{name}',
+                        'operation': 'list'}
         try:
             res = pfctl_table_op('f2b-jail/{remote_user}',
                                  table='f2b-{name}',
@@ -96,6 +99,7 @@ def create_app():
         except CalledProcessError as err:
             if err.stderr.find(b'pfctl: Table does not exist.') > 0:
                 res = []
+                reply.update({'error': f'\'{name}\' is not a known fail2ban jail'})
             else:
                 raise err
 
@@ -103,11 +107,9 @@ def create_app():
                   re.finditer(_PFCTL_TABLE_PAT,
                               '\n'.join([x.decode('ascii') for x in res]),
                               re.MULTILINE|re.VERBOSE)]
+        reply.update({'result': result})
 
-        return jsonify({'anchor': f'f2b-jail/{remote_user}',
-                        'table': f'f2b-{name}',
-                        'operation': 'list',
-                        'result': result }), 200 if len(res) else 404
+        return jsonify(reply), 200 if len(res) else 404
 
     @app.route("/register", methods=['PUT', 'DELETE'])
     @auth.login_required