Ahaggar: include an indent pointer in the plugin struct

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Ahaggar: use the indent_level ptr of the plugin struct

Instead of passing the indent level as an arugment, use the one provided
by the plugin data struct. This last one is global to all the node
walkers.

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Ahaggar: Just use the indent_level provided by the plugin struct

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>