with_timeout.py: reduced default timeout to 20 seconds

greentest/with_timeout.py

@@ -20,7 +20,7 @@ if sys.argv[1:2] and sys.argv[1]=='-t':
     TIMEOUT = int(sys.argv[1])
     del sys.argv[1]
 else:
-    TIMEOUT = 30
+    TIMEOUT = 20
 
 try:
     disabled_tests