Add custom step definitions for integration tests.

The Aruba cucumber library adds `lib` to the load path. However, it does
not auto load any files. Add a helper step to include this library so it
does not need to be required in each scenario.

Add a declarative step for checking the RSpec output from features.
Add JRuby settings to Aruba
Add wrap_env helper method.

Create a convenience helper method to wrap the environment for the
duration of a block. Non-existing variables will be set (stubbed) and
existing variables will be temporarily overwritten.

Add executable documentation explaining the behavior.
Run cucumber features with Travis.