Mirror selection should remove old mirrors for same repo
As described in https://bugs.alpinelinux.org/issues/4987 I had this
issue where one mirror was dead.
It was complicated by a lot due to the fact that re-running the
installer / fastest mirror detection and even selecting a mirror does
not remove the mirror selected at the last run.
To make it worse, the new one is added lower in the file and apk will
use the first (broken) one.
Until one manually fixes the apk/repositories file it’ll not be possible to install any more.
(from redmine: issue id 4988, created on 2016-01-04)