This MR brings some confort of use and of administration for the resiliency stack and resiliency related taks :

• logrotate some logs/feeds to save disk space
• adds more promises on export and import instances
• improves feedback on import failures : promises are more verbose, more information on the takeover webpage, ...
• better indempotency for the backup time information, which is now published instead of read from the .installed.cfg

Updated on 11/22 :

• improve pbs recipe : makes the trap command cross-shell
• remove infinite loops in scripts generated by pbs, but run a given amount of time until raising an error (which can be catched by promises)
• runner-importer script doesn't systematically fails if there is no requested SR.
• adds promises for notifier feeds (on exporter and pbs) to check last result and check if feed is corrupted

This MR should be merged after slapos.core has been upgraded