Mount /dev/pts in chroot

Mounting /dev/pts fixes mildly irritating errors during image creation,
i.e.: "Can not write log, openpty() failed (/dev/pts not mounted?)"
emitted by apt-get.

Change-Id: I4106bc584f1b29ce9283a20064bb5ae447f17fbe
Merge "Mount /dev/pts in chroot"