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.
Gotcha. I guess my next thought would then be: if we don't want to throw an IRE when "FloatingIPApi.create()" returns null but instead search through listed IP's (much like the caught IRE does now) then what do we want to do should both fail? It seems to me to throw an IRE!!! Do we want to let the null fall through which eventually gets us an NPE (wrapped in a RunNodesException)? It seems the IRE is more descriptive but maybe throwing an NPE with a detailed message will suffice?