'Take a list of API responses ("item"-portion only) and combine them.
Helper function to combine multiple aggegrated responses into a single
dictionary that resembles an API response.
Note: keys that don\'t have a \'list_name" key (including warnings)
are omitted.
:param   list_name: Name of list in dict.  Practically, this is
the name of the API called (e.g. \'disks\').
:type    list_name: ``str``
:param   response_list: list of API responses (e.g. resp[\'items\']).
Each entry in the list is the result of a
single API call.  Expected format is:
[ { items: {
key1: { api_name:[]},
key2: { api_name:[]}
:type    response_list: ``dict``
:return: dict in the format of:
{ items: {key: {api_name:[]}, key2: {api_name:[]}} }
ex: { items: {
\'us-east1-a\': {\'disks\': []},
\'us-east1-b\': {\'disks\': []}
:rtype:  ``dict``'

def _merge_response_items(self, list_name, response_list):

    merged_items = {}
    for resp in response_list:
        if ('items' in resp):
            for (k, v) in resp['items'].items():
                if (list_name in v):
                    merged_items.setdefault(k, {}).setdefault(list_name, [])
                    merged_items[k][list_name] += v[list_name]
    return {'items': merged_items}
