Harden ignite networking
Created by: eseliger
This PR improves the isolation of our executor VMs further by making them all fully isolated on the network.
# Test points:
- SSH into ignite VM
- curl -fv http://169.254.169.254/latest/meta-data/
- ssh 10.61.0.1
- curl -fv google.com
- curl -fvL http://10.0.1.4:5000 FAIL (will fix in tf module)
- ping 10.61.0.1
- ping 10.61.0.3 (other VM)
- ssh <host_internal_ip>
- ssh <host_external_ip>
Addresses https://github.com/sourcegraph/security-issues/issues/295
Test plan
See test points above, both tested on GCP and AWS.