Add support for multiple organizations in spacewalk.

I added some code to limit the inventory only to one organization within a spacewalk installation. The option -o takes the organization number. 
Also added the -p option to prefix the group names with the organization id, in case you use the script without -o and there are groups with the same name in more than one organization. Otherwise the groups would be merged to one big group in the inventory.

I hope you like the changes.