Add CB 3.0.0, CentOS 7

Note that current Vagrant (1.6.3) can't quite configure the networking
on RHEL7 correctly, and so it will bomb out with the second network
adapter unconfigured. To fix this manually:

    host$ vagrant ssh node1
    vm$ sudo ifconfig enp0s8 192.168.73.XXX netmask 255.255.255.0
    vm$ sudo service firewalld stop