Merge lp:~rbalint/livecd-rootfs/livecd-rootfs-autopkgtest-fix, w/ modifications

Only call sync, don't wrap kpartx and parse its output (doesn't appear to be
needed)

debian/changelog

@@ -5,6 +5,9 @@ livecd-rootfs (2.442) UNRELEASED; urgency=medium
     comparison prior to aa-series (LP: #1681548)
   * live-build/ubuntu-cpc/hooks/999-extras.binary: Exit on first failure
 
+  [Balint Reczey]
+  * sync before calling kpartx to let writing to loop devices finish
+
  -- Steve Langasek <steve.langasek@ubuntu.com>  Thu, 13 Apr 2017 10:38:04 -0700
 
 livecd-rootfs (2.441) zesty; urgency=medium

live-build/functions

@@ -13,6 +13,8 @@ apt-get -qqy install dosfstools gdisk
 clean_loops() {
 
     if [ -n "${backing_img}" ]; then
+        # sync before removing loop to avoid "Device or resource busy" errors
+        sync
         kpartx -v -d "${backing_img}"
         unset backing_img
     fi