Fix logging.

* src/cuirass/remote-server.scm (remote-server): Have stdout/stderr
line-buffered.
* src/cuirass/remote-worker.scm (remote-worker): Ditto.
* src/cuirass/remote.scm (publish-server): Discard publish logs.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>