Update pod-template to add a test_spec

Once this is finished, we should update pod-template's spec to include a test_spec:

``` ruby
spec.test_spec do |test_spec|
test_spec.framework 'XCTest'
test_spec.source_files = 'Tests/*.{swift,m,h}'
end
```

Also, add Quick/Expecta/Kiwi etc as a dependency here if used.

Start by locating pod-template and its existing specification and dependency declarations. Add the requested test_spec using XCTest and the Tests/*.{swift,m,h} sources, including Quick, Expecta, or Kiwi if the template uses one. Done means pod-template's spec contains the test configuration and required test dependency.

Written by the indexing model from the issue text.