Inter-rack slices with unbounded node-groups receive error

[kthare10]

Unbound NodeGroup when results in VMs spanning multiple sites results in error.

Refer https://github.com/RENCI-NRIG/exogeni/issues/225 for more details.

Such requests can be prevented by adding following rule:

 # nodeGroup validation - NodeGroups must provide domain
 [validateNodeGroup: (?v rb:validation on()) ->
     [ (?Z rb:violation error('NodeGroup Validation', 'NodeGroup must be bound to a site', ?X))
         <- (?R rdf:type req:Reservation), (?R col:element ?X),
         (?X rdf:type comp:ServerCloud), (?X dom:hasResourceType comp:VM),
         noValue(?X, req:inDomain) ] ]