s3:passdb/pdb_util make pdb_create_builtin consider whether backend deals with BUILTIN

s3:passdb/pdb_util make pdb_create_builtin consider whether backend deals with BUILTIN

when creating a BUILTIN group, make the strategy dependent on passdb backend behavior
1. if passdb is responsible for BUILTIN (normal case), call pdb_create_builtin_alias with gid=0 argument
so it asks winbindd for a gid to be used
2. if passdb is not responsible, ask for a mapping for the group first and let pdb_create_builtin_alias
create the mapping based on the gid that was determined in the mapping request

Pair-Programmed-With: Michael Adam <obnox@samba.org>

Signed-off-by: Christian Ambach <ambi@samba.org>
Signed-off-by: Michael Adam <obnox@samba.org>
Autobuild-User(master): Michael Adam <obnox@samba.org>
Autobuild-Date(master): Fri Jun 21 12:49:10 CEST 2013 on sn-devel-104