Improve trace_inputs.py to output a format easy to convert to gypi.

testing/xvfb.py

Index: testing/xvfb.py
diff --git a/testing/xvfb.py b/testing/xvfb.py
index a5cb7aa9d15b38740b79065fc4068adda96ca43a..73bcd1682fa1175b8b7b29baa4108bda209e2446 100755
--- a/testing/xvfb.py
+++ b/testing/xvfb.py
@@ -64,8 +64,13 @@ def wait_for_xvfb(xdisplaycheck, env):
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
         env=env)
+  except OSError:
+    print >> sys.stderr, 'Failed to load %s with cwd=%s' % (
+        xdisplaycheck, os.getcwd())
+    return False
   except subprocess.CalledProcessError:
-    print >> sys.stderr, 'Xvfb failed to load properly.'
+    print >> sys.stderr, (
+        'Xvfb failed to load properly while trying to run %s' % xdisplaycheck)
     return False
   return True