disable journald rate limiting

systemd-journald has rate limiting built in, but that's not sufficient
for the level of logging of OpenStack services during test
runs. Disable the rate limiting so that no log messages are lost.

Change-Id: I64599aba74c5a39276bb8f946cd236600b9cc81b
diff --git a/stack.sh b/stack.sh
index 2c10200..9fdb47e 100755
--- a/stack.sh
+++ b/stack.sh
@@ -748,6 +748,10 @@
 
 if [[ "$USE_SYSTEMD" == "True" ]]; then
     pip_install_gr systemd-python
+    # the default rate limit of 1000 messages / 30 seconds is not
+    # sufficient given how verbose our logging is.
+    iniset -sudo /etc/systemd/journald.conf "Journal" "RateLimitBurst" "0"
+    sudo systemctl restart systemd-journald
 fi
 
 # Virtual Environment