Tests, WebHost: add tests for host_room and minor cleanup

[black-sliver]

What is this fixing or adding?

• Tests behaviour that was added in #3496 and would've found the mistake that was fixed in #3603
• Tests that only the owner can see the log and queue commands
• Moves flask app init for tests to a common place (and ignores failure from double init)
• Create 1 flask client per test rather than per class
• Enables DEBUG for those, which allows printing the server traceback on failure
• Fix some typing and a typo in test_api_generate

How was this tested?

pytest, pytest-xdist