Create /etc/machine-id for RHEL images

Per the inline comment, a machine-id is required for kernels to
install correctly (this may well be a bug, but the linked issue
remained inconclusive).

Add a call to make the machine-id before install packages.

Change-Id: If75d04376e62bfdfe14ee3ca4d0bd5c8b383c1b0
Redhat-Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1737355

diskimage_builder/elements/rhel/pre-install.d/02-set-machine-id

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+# Set a machine-id.  The .qcow2 image doesn't have one, and sometimes
+# one will get made (if systemd is upgraded as part of the build
+# process) and sometimes not.  The problem is that certain kernel
+# install scripts bail silently without it; kernel packages end up
+# being installed but the initramfs etc isn't copied into place.
+#
+# Note this is cleared out in the sysprep role.
+#
+# See also:
+#  768c5e188c1b4bff01da14a49b96b51301db4c03 : similar thing for fedora
+#  https://bugzilla.redhat.com/show_bug.cgi?id=1737355 : upstream bug
+#  https://bugzilla.redhat.com/show_bug.cgi?id=1486124 : unresolved
+#   bug about kernel install requiring machine-id
+
+systemd-machine-id-setup