[FIX] #605 Saros doesn't reliably detect a broken internet connection

Saros will now detect broken connections.

TODO: their might be false positives during connection shutdown of the
remote side. As currently no hint is shown why the user is no longer
part of the session it does not matter.

Change-Id: Idcfcf5dbb6e1fd847c19b277af443f8ca5559191
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/946
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>