Default rlimit-nproc=3 causes problems with non-uid remapped containers

[lathiat]

By default, avahi-daemon sets the rlimit-nproc to 3.

The reasoning behind this is supposed to be security, to prevent avahi from launching processes in case of an exploit - though that is not really true since by default only 2 processes are consumed.

A problem arises when the same UID is user multiple times on the same system, this happens in particular when containers are used that do not remap UIDs into another range. In that case, a copy of avahi running in 2 containers causes the total process count to exceed 3 and Avahi cannot start.

References:
https://bugs.launchpad.net/maas/+bug/1661869
https://lists.linuxcontainers.org/pipermail/lxc-users/2016-January/010791.html
lxc/lxc#25