Add test targeting bugzilla bug 1116043

By default, the API client makes calls to the Foreman API with a content-type of
application/json. BZ bug 1116043 describes an issue that occurs if the
content-type if text/plain. Add a test which directly targets this bug.
Merge pull request #1060 from Ichimonji10/bugzilla

Add test targeting bugzilla bug 1116043