only return 1 network from api

[bshelton]

This should address #90

[linear]

CLO-489 VPC Network Peering Fails Due to Deleted Network Retention

According to this user, our terraform provider fails to provision peerings because it will list a network. I'm not sure but I think they mean the Network data source. We have an integration test for networks with the Terraform provider but don't have anything similar for the Network data source, so it's possible that's broken.

#90

[dgivens]

The API doesn't prohibit duplicate network names. If someone did have two networks with the same name, the data source would break for them.

I think this may need to change from returning a single network to a slice containing all available matching networks. I'm not sure what the correct way to handle that is in terms of Terraform, because that change in behavior is likely to cause problems for anyone using the data source when they upgrade.

[dgivens]

Discussed internally and we're going to create a new data source and deprecate the existing one so we don't break anyone who is already using the current data source by changing the behavior.

[TimSimpson]

Let's remove the new data source and the deprecation warning from the current data source which looks great as-is.

We don't need to create a new data source for a list of networks. I'm not a "product" guy but will venture that nobody wants to explicitly name their networks the same such that they could use such a list.

The catalyst for this PR was a user report that the network datasource would consider networks that had been deleted. The second non-explicitly called out problem was that if the data source found more than one network, it would return whichever one was arbitrarily seen first.

This PR fixes both errors by only looking at available networks and returning an error if things are ambiguous. I don't think we need to worry about breaking people who are relying on this behavior, as in most cases we will be helping them to avoid bugs (even if those bugs aren't happening to them yet).