avocado.job: Handle setup errors

If we have an error at test setup stage, avocado will
completely crash. This happens because the setup()
method is not properly wrapped inside the avocado
execution loop.

So, trust exception handling to the job level,
putting all test executions under a single try/except
block with appropriate status and test attribute handling.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #10 from lmr/fix-setup-errors

Fix setup errors