Securedrop: Write unit tests for manage commands

[arcrose]

Feature request

Description

The functions in manage.py are almost all marked with the # pragma: no cover to avoid having test coverage expect tests for them. There doesn't seem to be any particular reason why these shouldn't be tested.

[redshiftzero]

Great point @zsck. Tagging this one for 0.4.1. I also wonder if some of the functionality in manage.py could be DRYed up (e.g. both journalist.py and manage.py adds users).

[ghost]

https://github.com/freedomofpress/securedrop/pull/1850/files fixes a race and adds tests for one function. One step toward that goal ;-)

[heartsucker]

A regression during the work #1509 showed that we need tests for _run_from_commandline for each subcommand because args.func(args) may call a function that "forgets" to accept the CLI args object as the singular argument.