avocado.loader: Avoid uncaught exceptions while discovering jobs

Some very ugly modules use sys.exit() on imports. These are not catched
by Exception thus BaseException is required.

I did not omit KeyboardInterrupt as users get mad when ctrl+c doesn't
work. On the other hand nasty python code raising KeyboardInterrupt on
import can interrupt test-discovery (avocado list nasty.py => Interrupted
by user)
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/loader.py

@@ -135,7 +135,9 @@ class TestLoader(object):
         # Since a lot of things can happen here, the broad exception is
         # justified. The user will get it unadulterated anyway, and avocado
         # will not crash.
-        except Exception, details:
+        except BaseException, details:  # Ugly python files can raise any exc
+            if isinstance(details, KeyboardInterrupt):
+                raise   # Don't ignore ctrl+c
             if os.access(test_path, os.X_OK):
                 # Module can't be imported, and it's executable. Let's try to
                 # execute it.