Fix StatefulConnection to not to fail on exit

Some of the images require `tail` process to be explicitly stopped
after the `tail -f ... | nc ...` command has been executed and `nc`
process is finished. But most of the time `tail` process is ended
automatically that leads to fail of `killall tail` command.

Change-Id: I43c0b7781ca2ed98156e125566115196aab530cf
1 file changed