Fix up test data to match our expectations

Test data does not match the expectations, which is hidden in this
test code due to the way mocking of the edge_gateway works.

The next commit -- dependency injecting the Core::EdgeGateway.interfaces list
into the configuration -- changes how the mock is performed and highlights the
issue with the test data. Hence, fixing it up ahead of time to simplify the next commit.
Dependency inject interfaces into LoadBalancer gen

The LoadBalancerService generator was making several calls to the
EdgeGateway to look up interface details from a network_id.

This fixes this issue by instead injecting the EdgeGatewayInterface list
produced by Core::EdgeGateway.interfaces, as per ae14103d074 for NatService.
Remove redundant EdgeGateway test stub

Now that we inject the EdgeGateway  interfaces list into both
LoadBalancerService and NatService generators, we do not need to stub out
an edge_gateway object here.
Merge pull request #19 from alphagov/lb_dep_inject_2

[#65898110] LoadBalancerService generator dependency inject (redux)