Fix failing acceptance tests about terraform-provider-netbox

[fbreckle]

I get a pass for make testacc and the pipelines are green, too. I think all of these are happening to you, because you do not have a fresh netbox data volume, i.e. there is some leftover data in there.

If, for example, the IP 1.1.2.1/24 is already taken in your local volume, the "next available ip" in the prefix 1.1.2.0/24 will be 1.1.2.2/24 instead of the expected value. (2-5)
If you have some old testing interfaces and virtual machines in your netbox, the number of things that will be found in the tests is bigger than expected. (5-6)

Can you check if you have a similar problem with 1.?

[holmesb]

Yes passing now thanks, I've added a note to the readme explaining how to housekeep stale netbox data volumes

[fbreckle]

Closed by #102