'Get a total number of registerd users in the users list.
Args:
txn : Transaction object
Returns:
defer.Deferred: resolves to int'

def get_user_count_txn(self, txn):

    sql_count = 'SELECT    COUNT(*)    FROM    users    WHERE    is_guest    =    0;'
    txn.execute(sql_count)
    count = txn.fetchone()[0]
    defer.returnValue(count)
