Use limited IP address range in docker bridge

[stolpeo]

Describe the bug
Apparently the IP in the docker bridge change with every start. This caused a clash with our VPN.

3806: br-varfish: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
    link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    inet 172.29.0.1/16 brd 172.29.255.255 scope global br-varfish
       valid_lft forever preferred_lft forever

We need to limit the IP range if possible.