Busted now only provides the magic modules `assert`, `spy` etc for
the busted context. The helper module `spec/wibox/test_utils.lua`
therefore needs to explicitly require them.
Ref: https://github.com/awesomeWM/awesome/pull/139
This gets rid of awful.util.unittest and instead creates an automatic test for
it under spec/awful/util_spec.lua. In the process, it also fixes the test to
actually test the right thing and I took the liberty to add some more tests.
Signed-off-by: Uli Schlachter <psychon@znc.in>