Add rubocop lint checks

Executed by default rake task.
Remove StubFogInterface

I think this dates back to when the code was split from `vcloud-core` and
isn't strictly necessary anymore. Not using it here saves us another place
to maintain it and fixing the lint warnings relating to unused method
arguments.
Use eq() instead of == in spec tests

To fix lint warning `Operator == used in void context`.
Remove unused args from blocks

To fix lint warnings about unused arguments.
Fix whitespace in storage_profile_integration_spec

Indentation was off by 1~2 spaces. Fixes lint warning about misaligned end.
Replace assignment in condition for vApp

Use a separate variable and return early if we find an existing vapp. Create
a new vApp in a new variable if one doesn't exist. This should be clearer
than using the same variable for both and overwriting the nil value.
Replace assignment in condition for VM

Fixes lint warning. This isn't a whole lot more characters and is a little
bit more readable.
Merge pull request #22 from alphagov/70748484-rubocop_lint

[Fixes #70748484] Rubocop lint checks