Fix lvalert-overseer autorestart in container

overseer seems to always exit with an exit code of 0, which means
that 'autorestart=unexpected' does not restart it. So we set it
to 'true' instead.

docker/supervisord-lvalert-overseer.conf

@@ -10,4 +10,4 @@ stdout_logfile=/dev/stdout
 stdout_logfile_maxbytes=0
 redirect_stderr=true
 priority=2
-autorestart=unexpected
+autorestart=true