gpo: Initialize gp_ext variables in constructor

gpo: Initialize gp_ext variables in constructor

Initialize variables for the gp_ext in the
constructor instead of passing them via the parse
function.
This is a dependency of the "gpo: Implement
process_group_policy() gp_ext func" patch, since
the parse() function is now called by the ext,
instead of by gpupdate within apply_gp(). The
parse() function should only take the path
variable, to simplify writing Client Side
Extensions.

Signed-off-by: David Mulder <dmulder@suse.com>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>