Bitcoin daemon sends "Empty reply from server" when in test net
I leave it here. Because i spent about two days on it :-o
https://github.com/bitcoin/bitcoin/issues/10218


  Authentication is not optional. Configuring it yourself is optional, but bitcoind never accepts RPC connections without explicitly or implicitly configured username/password.


So, I just added user and pass from file /root/.bitcoin/.cache.
And get this:

curl --user __cookie__:96fea535b009e62ddffe1c6f5090c50396d17e7f96d0b0a75eb580bdd1771d29 --data-binary '{"jsonrpc":"1.0","id":"curltext","method":"getinfo","params":[]}' -H 'content-type:text/plain;' http://127.0.0.1:8332