JCLOUDS-607: ComputeService.createNodesInGroup throws NPE on FloatingIPA...

Addresses possible returned null value from 'FloatingIPApi.create()'. If upon check we find null then throw InsufficientResourcesException. This in turn will make a second check at IP allocation by iterating through 'FloatingIPApi.list()' and grabbing an available IP. If this subsequent call fails then re-throw InsufficientResourcesException.
I think `NodeAndNovaTemplateOptions` may be missing, but is there any reason it takes two AtomicRefs, rather than simply a Node and a NovaTemplateOptions object? I think having the NodeAndNovaTemplateOptions object in an AtomicRef should be enough?