Add network_1_id and network_2_id parameters

`network_1_id` is used by the vCloud Edge Gateway gem[1]; also add
`network_2_id` for later use and for consistency.

[1]:
https://github.com/alphagov/vcloud-edge_gateway/blob/8ccc1aa1617e4b2faf369a727716f0f19a76212d/spec/support/integration_helper.rb#L6
Fix capitalisation in CHANGELOG
Merge pull request #4 from alphagov/add-parameters

Add network_1_id and network_2_id parameters