Add unit tests for NetLaunch

This is the only project that didn't have unit test. Mostly because it's the
simplest - has no real logic of it's own, just uses Vcloud::Core. But it
would still benefit from having one. Mostly ripped off from Vcloud::Launcher
with the exceptions that:

- It calls describe on the object to be tested rather than namespacing it
  within a module as we plan to do for the other projects.
- Uses `let!` to separate variables from logic/expectations.
- It doesn't continue on errors like Vcloud::Launcher can.

It has the added benefit that:

- `rake spec` no longer executes all of the tests because the `Filelist[]`
  doesn't return any matches.
- We can make the testing section of the README look more like the other
  projects.
[#70513870] Standardise testing section in README

Same as alphagov/vcloud-core@c8a2318f33b12828416c3a963ad0462ff4d8f906
Merge pull request #19 from alphagov/70513870-readme_document_testing

[#70513870] Unit tests and standardise testing section in README.
Add rubocop lint checks

Executed by default rake task.
Remove StubFogInterface

This isn't used by this project. It's a hangover from when this project used
to live in the same repo as the other tools.
Remove unused args from blocks

To fix lint warnings about unused arguments.
Use eq() instead of == in spec tests

To fix lint warning `Operator == used in void context`.
Remove unused var assignment in NetLaunch

To fix lint warning:
```
lib/vcloud/net_launcher/net_launch.rb:22:13: W: Useless assignment to variable - net.
            net = Vcloud::Core::OrgVdcNetwork.provision(net_config)
            ^^^
```
Use be(true) instead of eq(true) in tests

I'm not sure there's strictly a difference. But since there's a specific
matcher for this we might as well use it and differentiate from the string
comparisons.
Change hash indentation in unit tests

To satisfy rubocop's complaints about:

    spec/vcloud/net_launcher/net_launch_spec.rb:12:8: W: end at 12, 7 is not aligned with let!(:network1)
    {{ at 5, 4
          }}
           ^

I don't strictly agree. But hey.