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.
[minor] please add a space after the `//` and add complete the "...after iterating through all available _" comment. Also, for the `if`, please use a 3-space indent and add spaces around the expression:
```
if (ip == null) {
   throw new InsufficientResourcesException("Failed to allocate a FloatingIP for node", e);
}
```