server: Refactor console setup to a separate function

server: Refactor console setup to a separate function

Also drop exec before the command, because it only causes troubles.
Thanks to dropping exec, we had to change the testsuite, because
without exec it starts a new process, which is not killed by "kill
$COPROC_PID" and since it holds a lock (via flock), we could not run
the following tests.

This change will be useful in next commits.