Compute MD5 hash of file.

def file_md5(self, file_name):
        """Compute MD5 hash of file."""
        file_contents = self._read_file(file_name)
        file_contents = file_contents + "\n"  # Cisco IOS automatically adds this
        file_contents = file_contents.encode("UTF-8")
        return hashlib.md5(file_contents).hexdigest()