build_wrapper: Add an error message when using an unknown license

Change-Id: I65858481d8e2b17ec923fe6ccf7e26a180eacdaf
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>
Use absolute file path for offline installer conf file as well

Make the handle_online_repository_build() read release description file
with absolute file path. Do not assume the conf file exists in the same
repository.

Change-Id: I80b08a019593bf9fcfed2ecdbbfb27b75b9b7569
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>