xenapi SimpleDH() is encoding password with a '\n' at the end

Kind of annoying, as we've had to go through a few iterations of fixes to get this right. However, it seems openssl behaves rather weirdly. When decrypting a base64 string, there needs to be a newline at the end. When you're encoding, it encodes everything sent, including a newline. The latter makes sense. The former... eh, I dunno. In any case, right now because we're always appending a newline when writing to stdin, openssl is encoding it with the password. We need to only send a newline when decoding base64 data.