Extend instance method ActivationKey.path

Allow a client to request the "releases" path from an activation key. This path
is in the following format:

    /activation_keys/<id>/releases

Add tests for this new functionality. Add the newly-created module of tests to
the API documentation.
Add tests targeting BZ bug 1112717

Check whether it is possible to create an activation key and fetch its releases.
Merge pull request #1147 from Ichimonji10/bz-1112717

Create test targeting BZ 1112717
Further refactor skip_if_bug_open

Move bug lookup logic out of `skip_if_bug_open` and into two new functions:

* `bz_bug_is_open`
* `rm_bug_is_open`

Create a solid battery of unit tests for these functions. Refactor existing,
nearby unit testing code.
Skip known failing tests

Use new method `bz_bug_is_open` to skip several known-failing tests. These tests
take advantage of the DDT module, and only some of the data passed in by the
`@ddt.data` decorator causes the test to fail. As a result, the usual
`@skip_if_bug_open` decorator is unsuitable, as it cannot selectively skip some
of the test generated by `@ddt.data`.