Mailman doesn't presently perform its own log rotation. We have
existing configuration to do this for mailman-web so add
mailman-core the same way.
There is also an outstanding bug that it lacks the capability to
release old log file handles when reopening them (e.g. at reload on
SIGHUP), so copytruncate method is strongly recommended. Luckily,
this is already the default for our logrotate role.
Change-Id: Ibd60b19e9d4eab3da49c399db163407a0eaaf604
9264794601