unittests: make directory structure more similar to current avocado

Try to maintain the directory structure closer to what is in the main
avocado project.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
functional test: introduce an initial version

This first test named like that (api) because it tests the exposed API.

One current limitation is that the provisioning of the API server is
rather manual, so the test can not be run fully automatically. In
the near future we intent to provision it automatically during test
setup.

Signed-off-by: Cleber Rosa <crosa@redhat.com>