Chroot deconfiguration should happen in the opposite order from chroot
configuration, so, for symmetry, undivert_grub should be called between
"lb chroot_debianchroot remove" and "lb chroot_sysfs remove".
This avoids us having apt cache files in the final image.
For auto/build, we move the call to clean_debian_chroot to the end,
this also takes care of the caches generated by apt-get update
in case of a preinstalled-pool.
For layered, it's just a simple swap of the lines.
LP: #1826377
grub-probe must not be called during image build so grub is diverted. In
multilayer image the chroot is always the tip of the filesystem, so we
divert grub at the beginning of each pass and undivdert it as the end.
For flat images, it's diverted just before building the chroot and
undiverted after.
Adds a function reduce_pass_size which removes duplicated files between
layers. A duplicate file is a file with same path, size, mode, owners
and content on 2 related layers.
lb_chroot_includes now takes the name of the pass as first argument and
will includes files for the corresponding pass from the directory
include.chroot.<pass>
