Remove ssh host keys when using simple init

In order for glean to operate properly and regenerate ssh host keys it
needs to start on a host without any ssh host keys. We hadn't been doing
this meaning that new host keys were not generated on images using
simple-init. Fix this by having simple-init delete any host keys found
in /etc/ssh late in the build process.

This should force glean/sshd to generate new host keys on first boot
depending on the distro.

Change-Id: Ic917387d92febf21c2cc37dfc1fa83fcf0c8e469

elements/simple-init/cleanup.d/90-remove-ssh-host-keys

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+# Cloud images shouldn't have ssh host keys baked
+# in so that they are regenerated on first boot and
+# are unique.
+
+# TODO(greghaynes) This should be a thing we do for all images, not just
+# simple-init.
+
+if [ -d /etc/ssh ] ; then
+    sudo find /etc/ssh -name 'ssh_host*' -type f -delete
+fi