`step` returns `nil` so it isn't suitable as a test in `try_for`.

At least with cucumber 1.3.8-1~bpo70+1, `step` always returns `nil`,
which corresponds to `false` when used as a boolean so the `try_for`
will never succeed. The return value of steps are indeed pretty much
considered undefined, so we instead refactor the test into a VM helper
function.
AppArmor: add rules to the system_tor profile, that are needed for bridges support.

Tor Launcher needs to rename and replace torrc.