887095 - cli locale was not set properly

Ok this patch completely replace ApiController.set_locale. It now properly parses locale coming from our CLI client and accept both UNIX locale format (cs_CZ) as well as HTTP standard one (cs-CZ).

Then it uses ApplicationController#extract_locale_from_accept_language_header method to properly find the right locale.

Also this patch correct ApplicationContoller#parse_locale method which is again instance method so it can access request environment and removes extract_locale_from_accept_language_header call from backend jobs (which will always return "en" anyway).

https://bugzilla.redhat.com/show_bug.cgi?id=887095
https://bugzilla.redhat.com/show_bug.cgi?id=896251