[pitivi] tests: Fix TestGnomeSystem test

[Thibault Saunier <tsaunier src gnome org>]

commit 3523f90e990c75ac771867a6ddcfcaf467b0e0e9
Author: Thibault Saunier <tsaunier gnome org>
Date:   Fri Jul 3 09:38:46 2015 +0200

    tests: Fix TestGnomeSystem test

 tests/test_system.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/tests/test_system.py b/tests/test_system.py
index df9153e..44c775d 100644
--- a/tests/test_system.py
+++ b/tests/test_system.py
@@ -96,7 +96,7 @@ class TestGnomeSystem(TestCase):
             # We can only test this on a Gnome system.
             return
 
-        if not self.system.session_iface.IsInhibited(
+        if self.system.session_iface.IsInhibited(
                 INHIBIT_LOGOUT | INHIBIT_USER_SWITCHING | INHIBIT_SUSPEND |
                 INHIBIT_SESSION_IDLE):
             # Other programs are inhibiting, cannot test.