apply 2-step upgrade to rancher

based on https://support.scc.suse.com/s/kb/360051866152?language=en_US, we shouldn't directly upgrade rancher from "2.n." to "2.(n+2)."

to handle the upgrade between 2.12 (in sylva 1.6) and 2.14 (in sylva 1.7) we need to apply the 2-step upgrade to rancher