test: fix printf format

tests/system-test/0-others/splitVGroup.py

@@ -242,9 +242,9 @@ class TDTestCase:
                     return False
 
         # warning performance
-        diff = (spend1 - spend2)*100/spend1
-        tdLog.info("spend1=%.2fs spend2=%.2fs diff=%.1f%%"%(spend1, spend2, diff))
-        if spend1 > spend2 and diff > 20:
+        diff = (spend2 - spend1)*100/spend1
+        tdLog.info("spend1=%.6fs spend2=%.6fs diff=%.1f%%"%(spend1, spend2, diff))
+        if spend2 > spend1 and diff > 20:
             tdLog.info("warning: the diff for performance after spliting is over 20%")
 
         return True