Edit description of lxc-container-mailserver-start and lxc-container-mailserver-stop

Summary: /usr/lib/systemd/system/lxc-containers.service became /usr/lib/systemd/system/lxc-container-mailserver.service

Reviewers: dereckson

Subscribers: dereckson, Kaliiixx

Differential Revision: http://devcentral.nasqueron.org/D132