mailman: allow user to configure paths instead of hardcoding them.

This is important in Gentoo Linux as the log file is in
/var/lib/mailman/log instead.
asterisk_*: remove dependency on Net::Telnet.

Since Telnet mode is not really used on these, convert them to just
use IO::Socket::INET as many other plugins use.

As there is no other component using Net::Telnet in the whole tree,
this removes one full dependency on the node itself.
asterisk_channels: fix name of plugin in configuration examples.