Send overseer logging to stdout

docker/supervisord-lvalert-overseer.conf

@@ -2,7 +2,7 @@
 command=lvalert_overseer -a %(ENV_LVALERT_USER)s -b %(ENV_LVALERT_PASSWORD)s
     -s %(ENV_LVALERT_SERVER)s -p %(ENV_LVALERT_OVERSEER_PORT)s
     -r %(ENV_LVALERT_OVERSEER_RESOURCE)s
-    -l /tmp/overseer_stdout.log -e /tmp/overseer_stderr.log
+    -l - -e -
 user=gracedb
 group=www-data
 stdout_logfile=/dev/stdout