Set 'INTERRUPTED' status for interrupted tests

If we press Ctrl+C, the test that was being executed
still does not have a status, and that reflects in the
job log with a None printed in the final status.

So, if there's no status yet, we should safely (?)
assume that the test was interrupted.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/test.py

@@ -399,6 +399,8 @@ class Test(unittest.TestCase):
                            self.fail_reason)
 
         else:
+            if self.status is None:
+                self.status = 'INTERRUPTED'
             self.log.info("%s %s", self.status,
                           self.tagged_name)