fc-agent: the automatic management task that runs every ten minutes now only
switches to the new system configuration if it actually has changed with the
last build. We already used that behaviour on the 15.09 platform.
This saves some CPU time and avoids frequent ACME certificate renewal checks
which also trigger unneccessary Nginx reloads (#PL-129745).
Fix ACME certificate validity check for multiple virtual hosts. SNI was not
used so only the certificate for the default vhost was monitored (#PL-129749).
Fix link in /etc/local/firewall/README (#PL-129735).
Improve our backup using multiple queues and more workers to balance fast and
slow backups and reduce head of line blocking issues that cause unnecessary
delays under stress (PL-128789).