oeqa: tear down oeqa decorators if one of them raises an exception in setup

Some of the decorators need proper cleanup, such as OETimeout
which sets a signal handler that needs to be cleared via teardown.
If this is not done then the signal gets called later with unpredictable effects.

This can be seen if there's a test that is skipped via a decorator and sets a timeout
at the same time: the timeout isn't cleared, and is invoked later in a
completely unrelated context. The test case for this is added in the
next commit.

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>