Check text file exisitense.

    Argument:

        filename: text file of bulk updating

def check_infile(filename):
    """Check text file exisitense.

    Argument:

        filename: text file of bulk updating
    """
    if os.path.isfile(filename):
        domain = os.path.basename(filename).split('.txt')[0]
        return domain
    else:
        sys.stderr.write("ERROR: %s : No such file\n" % filename)
        sys.exit(1)