Error generating environment and network for OOB in racks

[marcusgc]

When OOB environment have more than one network prefix configured, networkapi is raising error
when trying to allocate networks and vlans for rack.
Instead of looking for an available network in network prefixes, it is trying to get "nth" network in all network prefix configured for environment.
If prefix is shorter than rack number, it will raise "list index out of range". If all prefixes have nth network available, it will allocate more than one necessary networks.

If should just look for an available network in all available prefixes.