meta/lib/oeqa/core/tests/cases/timeout.py: add a testcase for the previous fix

This is the sequence that didn't properly operate:

- a test case that skips and isn't executed
- a second test case that is skipped via a dependency decorator, and sets a timeout
- a third test case that takes longer than the timeout from the second
test case

Without the fix, the timeout is not cleared, and the third test case is
erroneously aborted. With the fix, the timeout is cleared and the third
test case is able to complete.

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 54ef07a9)
Signed-off-by: Steve Sakoman <steve@sakoman.com>