param: Add non-global smb.cfg option (support 2 different smb.confs)

param: Add non-global smb.cfg option (support 2 different smb.confs)

The default behaviour is that there is only a single global underlying
LoadParm object. E.g. if you create 2 different LoadParm objects in
python, they both modify the same underlying object.

This patch adds a mechanism to override this and create a separate
non-global LoadParm object. The use-case is the backup tool, where we
want to manipulate 2 different smb.conf files (the one used to create
the backup, and the smb.conf in the backup itself).

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>