If we change output mode on remote machine via
text-based session

 node a (server)
 ------
 require('console').listen('unix/:/tmp/X.sock')
 ...

 node b (client)
 ------
 require('console').connect('unix/:/tmp/X.sock')
 connected to unix/:/tmp/X.sock
 ...
 unix/:/tmp/X.sock> \set output lua

the client get stuck forever, it is because the text
wire protocol waits for yaml eos terminator which of
course never hit the peer, because lua mode uses own
one.

Thus to fix this problem we have to preprocess the text
we're passing to the server, just like we do in local
console. So we reuse command parsing code and remember
current output terminator in text_connection_mt instance.

Another problem is that named default output mode. There
could be a mixed environment where server operates in
default lua mode but client connects with yaml mode. To
break a tie we yield "\set output" command with current
output mode when establishing a connection. Since the
output format is per-session bound this doesn't affect
any other connections on a server.

Part-of #3834

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
(cherry picked from commit c358398c)