Change the customization directory

Change the customization directory

The current customization directory is
“$sysconfdir/ganeti/instance-debootstrap.d”. Recently, the variants
support has added the variants configuration as
“$sysconfdir/ganeti/instance-debootstrap/variants/default.conf”. This
means we have two, very similar (instance-debootstrap.d vs.
instance-debootstrap) directories under ganeti.

This patch changes the customize directory to
$sysconfdir/ganeti/instance-debootstrap/hooks. It is more in line with
Ganeti's own hooks naming, and removes the old “.d” directory, for a
more sane layout.

People upgrading, with the default (commented-out) CUSTOMIZE_DIR will
need to rename their on-disk directory.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>