smoke tests for UI
Merge pull request #1244 from sghai/smoke-ui

Smoke tests for UI
Add a test subscribing a system to a content view

Add a new test module: `tests.foreman.api.test_contentview_v2`. Add a test to
this module which does the following:

1. Create an organization, lifecycle environment and content view.
2. Publish the newly created content view.
3. Promote the newly published content view.
4. Create a system which references the organization, lifecycle environment and
   content view.

Update the following methods:

* `ContentView.publish`
* `ContentViewVersion.promote`

Make these two methods raise an exception if an HTTP 4XX or 5XX response is
received, or return decoded JSON data otherwise. Update all usages of those
methods.