Add hooks to ubuntu-cpc to divert /bin/sync in the chroot and undivert it

at the end.  This is a general-purpose change that should be applied to
all flavors and archs, but at the moment it's only needed on armhf+raspi2
to work around the raspberrypi2-firmware postinst calling sync, which is
actually warranted in the normal case.

debian/changelog

@@ -6,6 +6,11 @@ livecd-rootfs (2.376) UNRELEASED; urgency=medium
   [ Steve Langasek ]
   * Drop BuildLiveCD from the examples; we now use launchpad-buildd to drive
     livefs builds, so BuildLiveCD is obsolete and misleading.
+  * Add hooks to ubuntu-cpc to divert /bin/sync in the chroot and undivert it
+    at the end.  This is a general-purpose change that should be applied to
+    all flavors and archs, but at the moment it's only needed on armhf+raspi2
+    to work around the raspberrypi2-firmware postinst calling sync, which is
+    actually warranted in the normal case.
 
  -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Thu, 04 Feb 2016 17:31:18 +0100
 

live-build/ubuntu-cpc/hooks/001-divert-sync.chroot_early

@@ -0,0 +1,13 @@
+#!/bin/sh
+set -e
+
+ARCH=$(dpkg --print-architecture)
+
+dpkg-divert --quiet --add --divert /bin/sync.REAL --rename /bin/sync
+cat > /bin/sync <<'EOF'
+#! /bin/sh
+echo "$0: diverted by livecd-rootfs" >&2
+exit 0
+EOF
+
+chmod +x /bin/sync

live-build/ubuntu-cpc/hooks/999-undivert-sync.chroot

@@ -0,0 +1,5 @@
+#! /bin/sh
+set -e
+
+rm -f /bin/sync
+dpkg-divert --quiet --remove --rename /bin/sync