engine: docs internal server error

- If you try to load a manual document in a locale that
  doesn't exist, the server would throw a 500 due to a
  problem in the setup of path of the DocsServlet. This
  patch fixes that issue.
- If you try to load a manual document in a locale that
  doesn't exist, you will get a 404 instead of a warning
  message that the language is not available.
- Fixed issue in the path of the link that would forward
  you to the english documentation.
- Fixed issue in the cookie path that would store if you
  had been shown the warning message yet.

Change-Id: I3036d05e736a4bc2603423fb7041910a9daa1472
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1083528
Signed-off-by: Alexander Wels <awels@redhat.com>