If you get this error in the build log:
########## LOG START ##########
Template => not found linux-centos-7.0.1406-x86_64-min-gen2-v2
The above is an example, all you need to do is on the slave open the port: 5656.
Centos 7
firewall-cmd --zone=public --add-port=5656/tcp --permanent
firewall-cmd --reload
Centos 6
iptables -I INPUT -p tcp -m tcp --dport 5656 -j ACCEPT
service iptables restart