* urlgetter: fix tunnel test
This diff fixes the urlgetter test suite to make sure we
are correctly testing for tunnel creation.
While there, improve the way in which we create a testing
directory and add a test for that.
Part of https://github.com/ooni/probe/issues/985.
* fix comment
* fix comment
This functionality should be helpful to test that the general
interface of the tunnel package is okay from the engine package.
Part of https://github.com/ooni/probe/issues/985