[helpers] Add loop information parsing

The format is:

"loop": {
    "input": {
        "type": "data_format_name"
    },
    "output": {
        "type": "data_format_name"
    }
}

beat/backend/python/helpers.py

@@ -77,6 +77,10 @@ def convert_experiment_configuration_to_container(config):
     else:
         data['result'] = { 'channel': config['channel'], 'path': config['result']['path'] }
 
+    if 'loop' in config:
+        data['loop'] = \
+            dict([(k, { 'channel': v['channel'], 'path': v['path'] }) for k,v in config['loop'].items()])
+
     return data