* Ship alt-common-els-rollout.repo with the els-alt-1..6 gradual-rollout slots (enabled) and their -bypass counterparts (disabled), so the ALT slot rollout reaches clients gradually instead of only at graduation to stable * postinst: write /etc/apt/sources.list.d/alt-common-els-rollout.list with the els-alt-1..6 gradual-rollout slots on rollout.alt.tuxcare.com (active) and their slot-N-bypass counterparts (commented out); the rollout host has no channel segment and takes no credentials, so no /etc/apt/auth.conf.d entry is added. postrm removes the file. (ELS-2641) * %post now pins $releasever in alt-common-els.repo too, not just the rollout file: the Amazon Linux 2 branch only covered the stable repo on AL2, so a plain el7 host reporting 7Server or 7.9 still asked for el/7Server/ (ELS-2334)