Run udevadm settle after kpartx -l

it may happen that if the system where disk-image-create runs is busy,
then the kpartx -l run may leave a stale autodelete loop device.

This is because kpartx -l first adds a new loop device, then does the
listing and removes the loop device. The latter may not end before the
end of the kpartx run, leaving a loop device marked as autodelete.
Such kind of loop device will automatically delete itself, so the
 rm -r $WORKING
after
 sudo umount -f $WORKING/mnt
in the EXIT trap will fail because $WORKING does not exist anymore.

To prevent this situation, just ask udev to finish its operations,
properly removing the (temporary) loop device.

Change-Id: I12246f3dbe6b5669e698767682a5a142f803823b

elements/redhat-common/bin/extract-image

@@ -54,6 +54,7 @@ function extract_image() {
             qemu-img convert -f qcow2 -O raw $CACHED_IMAGE $WORKING/$RAW_FILE
 
             ROOT_PARTITON=p$(sudo kpartx -l $WORKING/$RAW_FILE | awk "/loop[0-9]+p/"|wc -l)
+            sudo udevadm settle
 
             # kpartx fails if no /dev/loop* exists, "losetup -f" prints first unused
             # loop device and creates it if it doesn't exist