Get list of all subscriptions to a specific topic.

    CLI example to delete a topic::

        salt myminion boto_sns.get_all_subscriptions_by_topic mytopic region=us-east-1

def get_all_subscriptions_by_topic(name, region=None, key=None, keyid=None, profile=None):
    '''
    Get list of all subscriptions to a specific topic.

    CLI example to delete a topic::

        salt myminion boto_sns.get_all_subscriptions_by_topic mytopic region=us-east-1
    '''
    cache_key = _subscriptions_cache_key(name)
    try:
        return __context__[cache_key]
    except KeyError:
        pass

    conn = _get_conn(region=region, key=key, keyid=keyid, profile=profile)
    ret = conn.get_all_subscriptions_by_topic(get_arn(name, region, key, keyid, profile))
    __context__[cache_key] = ret['ListSubscriptionsByTopicResponse']['ListSubscriptionsByTopicResult']['Subscriptions']
    return __context__[cache_key]