New test: abort -- calls abort() and abort test.

It actually triggers a bug in the current implementation of Avocado.
The tests doesn't return a status or update the interface:

<pre>
DEBUG LOG: /home/rmoura/avocado/logs/run-2014-07-16-18.56.54/debug.log
TOTAL TESTS: 1
(1/1) abort.1: 
</pre>

Because the forked test process becomes defunct:

<pre>
rmoura   21434 20594  4 18:56 pts/0    00:00:00 python ./scripts/avocado run abort
rmoura   21489 21434  0 18:56 pts/0    00:00:00 [python] &lt;defunct>
</pre>

Signed-off-by: Ruda Moura <rmoura@redhat.com>