Check to see if an SNS topic exists.

    CLI example::

        salt myminion boto3_sns.topic_exists mytopic region=us-east-1

def topic_exists(name, region=None, key=None, keyid=None, profile=None):
    '''
    Check to see if an SNS topic exists.

    CLI example::

        salt myminion boto3_sns.topic_exists mytopic region=us-east-1
    '''
    topics = list_topics(region=region, key=key, keyid=keyid, profile=profile)
    return name in list(topics.values() + topics.keys())