After you have installed a CentOS 7 LXC template on a systemd supprted distro (Fedora 21/22, CentOS 7 with LXC 1.0.7), you can experience a ultra slow container boot (more than 5 minutes!). A small change can fix this issue.
In the container config (i.e.
lxc.include = /usr/share/lxc/config/centos.common.conf
lxc.include = /usr/share/lxc/config/fedora.common.conf
This will make the container boot fast as it should be.
centos.common.conf is fine for CentOS 6 but not for CentOS 7: CentOS 7 is based on Fedora 19 and uses systemd, thus
fedora.common.conf is the right config file to use.