test(pageObjects): Added rxEnvironment Page Object

Added a page object for rxEnvironment. getEnv returns the current environment.
Anonymous helper functions don't need to use Astrolabe. See [rxDiskSize](https://github.com/rackerlabs/encore-ui/blob/3802059c3f52b9d99e0866d07a87ed78551614da/src/rxDiskSize/rxDiskSize.page.js#L1-L2), for instance.