scripts: add "release with rkt"
scripts: add "release with rkt"

This script uses rkt and a fedora image to build release tarballs.

squeed/plugins,containernetworking/cni,rosenhouse/cni,achanda/cni,squaremo/cni,rosenhouse/cni,achanda/cni,containernetworking/plugins,kad/cni,luxas/cni,squeed/plugins,tomdee/cni,steveeJ/cni,dcbw/cni,luxas/cni,murat1985/cni,containernetworking/cni,murat1985/cni,mcastelino/cni,steveeJ/cni,tangle329/cni,kad/cni,dcbw/cni,appc/cni,tangle329/cni,squaremo/cni,containernetworking/plugins,appc/cni,tomdee/cni,mcastelino/cni