On you HOST filesystem

mkdir /var/lib/libvirt/lxc/centos-6-x86_64/etc/yum.repos.d/ -p
cat /etc/yum.repos.d/CentOS-Base.repo |sed s/'$releasever'/6/g > /var/lib/libvirt/lxc/centos-6-x86_64/etc/yum.repos.d/CentOS-Base.repo
yum groupinstall core --installroot=/var/lib/libvirt/lxc/centos-6-x86_64/ --nogpgcheck -y
yum install plymouth libselinux-python --installroot=/var/lib/libvirt/lxc/centos-6-x86_64/ --nogpgcheck -y

On the CHROOTED environment
chroot /var/lib/libvirt/lxc/centos-6-x86_64/
echo password |passwd root --stdin

#Fix root login on console
echo "pts/0" >>/etc/securetty
sed -i s/"session    required     pam_selinux.so close"/"#session    required     pam_selinux.so close"/g /etc/pam.d/login
sed -i s/"session    required     pam_selinux.so open"/"#session    required     pam_selinux.so open"/g /etc/pam.d/login
sed -i s/"session    required     pam_loginuid.so"/"#session    required     pam_loginuid.so"/g /etc/pam.d/login

#Configuring basic networking
cat > /etc/sysconfig/network << EOF
NETWORKING=yes
HOSTNAME=lxc1.test.centos.org
EOF

cat > /etc/sysconfig/network-scripts/ifcfg-eth0 << EOF
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
EOF

#Enabling sshd
chkconfig sshd on

# Fixing root login for sshd
sed -i s/"session    required     pam_selinux.so close"/"#session    required     pam_selinux.so close"/g /etc/pam.d/sshd
sed -i s/"session    required     pam_loginuid.so"/"#session    required     pam_loginuid.so"/g /etc/pam.d/sshd
sed -i s/"session    required     pam_selinux.so open env_params"/"#session    required     pam_selinux.so open env_params"/g /etc/pam.d/sshd

cat > /etc/fstab << END
/dev/root               /                       rootfs   defaults        0 0
none                    /dev/shm                tmpfs    nosuid,nodev    0 0
END

cat > /etc/init/lxc-sysinit.conf << END
start on startup
env container

pre-start script
        if [ "x$container" != "xlxc" -a "x$container" != "xlibvirt" ]; then
                stop;
        fi
        initctl start tty TTY=console
        rm -f /var/lock/subsys/*
        rm -f /var/run/*.pid
        telinit 3
        exit 0;
end script
END

#Exit the chroot
exit

TAR the root filesystem
cd /var/lib/libvirt/lxc/centos-6-x86_64
tar cvf centos-6-x86_64_lxc.tar .