simplify continue_or_skip
call "yum upgrade" before upgrade

Sometimes there is bug in rpm scriplets and it is find only when new release comes out and new version is pushed to previous release of fedora.
For example
https://bugzilla.redhat.com/show_bug.cgi?id=844167
So it makes sense to upgrade to most recent packages in Fedora N before upgrading to Fedora N+1
add GPG keys