Investigate a potentially missing depdendency

[nathandyer]

Description

During a recent SD install to a freshly provisioned server running Ubuntu Server 20.04.6, the ./securedrop-admin install process ran into an error during the run, citing that the /etc/iptables directory was missing and that it couldn't continue.

To workround this, I had to do an apt install iptables-persistent on the server, at which point ./securedrop-admin install was able to complete the installation without issue.

We should determine if this is a required package, and if so, add it as a dependency.

Steps to Reproduce

1. Install a fresh copy of Ubuntu Server 20.04.6 and configure it according to the SD docs
2. Copy SSH keys from the Admin Workstation to it
3. Run ./securedrop-admin install (along with setup and sdconfig beforehand, if necessary)

Expected Behavior

The install happens without issue.

Actual Behavior

An error regarding a missing /etc/iptables directory that stops the installation.

Comments

Not sure if this was a one-off, and also not sure of any potential security concerns about the iptables-persistent package.