Added config option DISABLE_EXPORTS_SETUP for sites without proper control

of their file server (aero)

Extend DISABLE_NAMED_SETUP: when set, we don't set a nodes hostname to
<name>.<eid>.<pid>.<domain> since that won't resolve.  Just stick with
pc<XXX>.<domain> in those cases.  The various sethostname* scripts are
now .in so that they get preprocessed to check for the option.