Comment 12 for bug 1741096

that had some noise:
 === modified file 'bin/mount-image-callback'
--- bin/mount-image-callback 2018-01-03 15:44:47 +0000
+++ bin/mount-image-callback 2018-01-04 18:08:43 +0000
@@ -284,6 +284,10 @@

  debug 1 "connected $img_in ($fmt) ${rwmode} to $nbd. waiting for device."
  i=0
+ local out=""
+ out=$(blockdev --rereadpt "$nbd" 2>&1) ||
+ debug 1 "blockdev rereadpt $nbd failed"
+ udevadm settle
  while i=$(($i+1)):; do
   get_partition "$nbd" && nptnum="$_RET" && break
   [ $i -eq 40 ] && {