Add API tests for LifecycleEnvironment and GPGKey

Add several API tests which target the following URLs:

* `katello/api/v2/gpg_keys`
* `katello/api/v2/environments`

Many tests were already in place for GPG keys. However, there was no test for
issuing a GET to `katello/api/v2/gpg_keys`. This commit fixes that. In contrast,
there were no tests for lifecycle environments, and this commit adds a basic set
of HTTP POST and GET requests for lifecycle environments.
This API test is POSTing to the same URL that you've listed. If a web browser is posting to here:

    /katello/api/v2/gpg_keys?order=name+ASC&organization_id=1&page=1&paged=true&search=

Then that means that the URL being POSTed to is this:

    /katello/api/v2/gpg_keys

And everything else is just a bunch of arguments being sent to that URL.