Right now, post-up interface routes are semi-hardcoded for the production.
This changes allows to define for the staging area some more setup.
As in for example the following for the staging area gateway:
--- networks: default: interface: eth0 address: 192.168.100.125 netmask: 255.255.255.0 gateway: 192.168.100.1 ups: 'iptables -t nat -A POSTROUTING -s 192.168.128.0/24 -o eth0 -j MASQUERADE' downs: 'iptables -t nat -F' private: interface: eth1 address: 192.168.128.1 netmask: 255.255.255.0 ups: [] downs: []