rspec and aws-sdk-core have changed!

We started getting this error in our jenkins deployer script:

```
dumbwaiter-0.5.3/lib/dumbwaiter/stack.rb:14:in `find': undefined method `new' for Aws::OpsWorks:Module (NoMethodError)
```

When we ran the dumbwaiter test suite, it would not run because its and collection matchers were moved out of  rspec. So we added `rspec-its` and `rspec-collection_matchers` to development dependencies.

Once the test suite was running, we changed the call to `Aws::Opsworks.new` to `Aws::Opsworks::Client.new` to keep up with the latest version of `aws-sdk-core`. You can see the central change to the test suite [here](https://github.com/sharespost/dumbwaiter/compare/minifast:master...master#diff-76a1c12e1283c797bf078d390041c9c0R11).