add script for retagging foreman-nightly-* into katello-thirdparty-foreman-*

This script MUST be run from katello.git/rel-eng/ directory
It take latest builds from foreman-nightly-* tag and re-tag them
into katello-thirdparty-foreman-* tag.
It does that for ever package listed in comps-katello-foreman-server-*.xml
and for every build, which is newer in foreman-nightly-* compared to equivalent
build in katello-thirdparty-foreman-*
Merge pull request #2464 from xsuchy/pull-req-retagging

add script for retagging foreman-nightly-* into katello-thirdparty-forem...