See merge request nexedi/slapos!1433

  https://archive.fosdem.org/2023/schedule/event/innodb_change_buffer/
  https://jira.mariadb.org/browse/MDEV-27734
  https://mariadb.com/kb/en/innodb-change-buffering/

If a server reboots brutally, there will be a legacy httpd pid file stay
in the file system, and the OS may reuse the PID that remains in that
file, which will cause httpd service to fail to start even if there is
no such httpd service is running.

This commit implemented the following logic:
0. If there is no existing PID file, then run the httpd service directly
1. If the PID file exists and contains the PID used by another process,
we delete the PID file, then restart the httpd service
2. If the PID file exists and contains the PID used by another running
httpd service, we allow the httpd report the "already running" error
normally

This is the last version supporting python 2.7.

See merge request nexedi/slapos!1428

See merge request !1404

- activate cu_config_link parameter
- update cu-config.xml
- add supervision log and nc session log