Use "resource" for the GLUE2GroupID

Altough using "cloud" would seem OK, we have to use "resource" so as to
get the information included in the site-BDII.

Refers #1
Do not set the GLUE2DomainID on the DN if not needed

The GLUE2DomainID=SITE in the DN is only needed if the node is also a
site-BDII so we should not set this if it is not needed.

Closes #1