[pitivi] tests: Make the 'mock missing' reported error more readable

[Thibault Saunier <tsaunier src gnome org>]

commit d8e0445e3d2dc4fdfb7a0c1b3931576d6f9fafc7
Author: Thibault Saunier <tsaunier gnome org>
Date:   Tue Apr 1 10:20:26 2014 +0200

    tests: Make the 'mock missing' reported error more readable

 tests/runtests.py |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/tests/runtests.py b/tests/runtests.py
index a83dd56..68178ae 100644
--- a/tests/runtests.py
+++ b/tests/runtests.py
@@ -60,8 +60,9 @@ def setup():
 
     try:
         import mock
-    except ImportError as e:
-        raise Exception("Python mock library missing! www.voidspace.org.uk/python/mock", e)
+    except ImportError:
+        print("\n\nPython mock library missing! www.voidspace.org.uk/python/mock\n\n", file=sys.stderr)
+        raise
 
 
 if __name__ == "__main__":