Check to see if an SNS topic exists.

    CLI example::

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

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

    CLI example::

        salt myminion boto_sns.exists mytopic region=us-east-1
    '''
    topics = get_all_topics(region=region, key=key, keyid=keyid,
                            profile=profile)
    if name.startswith('arn:aws:sns:'):
        return name in list(topics.values())
    else:
        return name in list(topics.keys())