Use current python in internal_test.py

Change-Id: I2035a32c100ab2ed8cba0171405ac87f1653d315
diff --git a/tools/internal_test.py b/tools/internal_test.py
index cc2ee93..8e03610 100755
--- a/tools/internal_test.py
+++ b/tools/internal_test.py
@@ -340,6 +340,10 @@
 def execute(cmd, archive, env=None):
   if cmd == []:
     return
+  
+  assert(cmd[0].endswith('.py'))
+  cmd = [sys.executable] + cmd
+
 
   utils.PrintCmd(cmd)
   with utils.TempDir() as temp: