MDL-48144 upgrade: add v2.8.0 sep lines
Merge branch 'MDL-48144' of git://github.com/stronk7/moodle
MDL-48174 core_lang: support for ->skiplangupgrade in lang cron task

Similar to upgrade_language_pack(), update_langpacks_task should
respect skiplangupgrade config. Also, this should be added to behat
whitelist, so it can be disabled during on-sync period, when lang
pack for master is not available.