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.
And therein lies the million dollar question! Because most of the code to allocate, based on "listed" IP's, is inside the catch I left it there and I think it makes sense to do so. Should something pop we'd like a last-effort-attempt to allocate an IP by iterating through the listed IP's. This code is basically a short-circuit to get us there should the call to ".create()" give us a null. Why the call to ".create()" returns null (though I don't believe for all cases/providers) but the call to ".list()" succeeds ... I've no idea.