Comment 4 for bug 1491750

We should add check to verify that sysctl contains values
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

Check should be performed with MULTIPLE_NETWORKS feature.
The point is where to set that check - in environment creation or before each test.
Seems that only after environment creation is not enough because after restart settings may not apply and user still have environment without
net.bridge.bridge-nf-call-ip6tables = 0