vifib-server: Increase memlock from default 64K to 64M
Wendelin.core 2 tests need to be able to mlock 64M to run. Increase corresponding limit for all subprocessed spawned by cron, which covers slapos -> supervisord -> ...
See added comments in slapos_limit.conf for why this has to be done in /etc/security/limits.d/slapos.conf instead of /etc/systemd/system/cron.service.d/override.conf
I testd this to work on a KVM of mine with manually putting /etc/security/limits.d/slapos.conf in place. Before the patch:
https://erp5.nexedi.net/test_result_module/20201009-341BCC3C/17 (lots of "OSError: [Errno 1] Operation not permitted" for mlock requests)
After the patch:
https://erp5.nexedi.net/test_result_module/20201009-6B97A93B/17 (test.wcfs/fs passes correctly)