set a maximum systemd journal size

We've noticed a trend with deploys where we seem to use up all of the
free space in the ramdisk, and this could distinctly be systemd.

While we're not logging it, we odn't need infinite logs either because
the default pattern is likely to consume quite a bit more space than we
would like to use.

As such, set a max size.

Related-Bug: 2116135
Change-Id: Iae94278640d79232ec66402c799e4bd6e42336df
Signed-off-by: Julia Kreger <juliaashleykreger@gmail.com>

dib/ironic-python-agent-ramdisk/README.rst

@@ -25,6 +25,9 @@ Beyond installing the ironic-python-agent, this element does the following:
   listen for raw data from stdin and write compressed data to stdout. Command
   can be with arguments.
 * Configures rescue mode if ``DIB_IPA_ENABLE_RESCUE`` is not set to ``false``.
+* By default, sets a maximum size for the ramdisk systemd journal to 15M. This
+  can be disabled by setting ``DIB_IPA_DISABLE_JOURNAL_MAX_LOG_SIZE`` to any
+  value which is not ``False``.
 
 This element outputs three files:
 

dib/ironic-python-agent-ramdisk/post-install.d/98-set-journal-config

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+if [ "${DIB_DEBUG_TRACE:-0}" -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+DIB_IPA_DISABLE_JOURNAL_MAX_LOG_SIZE=${DIB_IPA_DISABLE_JOURNAL_MAX_LOG_SIZE:-False}
+
+if [[ "$DIB_IPA_DISABLE_JOURNAL_MAX_LOG_SIZE" == "False" ]]; then
+    # Default templates have a journal section already defined, and we don't use
+    # iniset by convention, so unless we really need to, we'll just append here.
+    echo "SystemMaxUse=15M" >> /etc/systemd/journald.conf
+fi