Calculate md5 checksum on file

    :param filepath: Full path to file (e.g. /home/stack/image.qcow2)
    :type  filepath: string

def file_checksum(filepath):
    """Calculate md5 checksum on file

    :param filepath: Full path to file (e.g. /home/stack/image.qcow2)
    :type  filepath: string

    """
    checksum = hashlib.md5()
    with open(filepath, 'rb') as f:
        for fragment in iter(lambda: f.read(65536), ''):
            checksum.update(fragment)
    return checksum.hexdigest()