The securedrop-app-code package dependencies are incomplete

[rmol]

Description

When folding mod_wsgi into the securedrop-app-code package, its apt dependencies should have been added as well. The omission of libpython3.5 could cause the installation of securedrop-app-code to fail, as Apache wouldn't be able to load mod_wsgi due to the missing shared library. This was missed because libpython3.5 is installed as part of the ubuntu-server metapackage when following the usual SecureDrop server installation. It should be explicitly required.

Steps to Reproduce

Remove libpython3.5 from a working staging or production VM and restart the Apache service.

Expected Behavior

That you wouldn't be able to remove libpython3.5 without also having to remove securedrop-app-code, or since that's possible, that the SecureDrop services would continue to work.

Actual Behavior

Apache fails to restart because of the missing shared library from libpython3.5.

Comments

The securedrop-app-code dependencies just need to be better specified.