Python 3 compatibility: convert raw_input to input

Change-Id: I86699cc6d880c137e80183d7196874ed0f7803e6

labs/st.py

@@ -13,6 +13,7 @@ import importlib
 import logging
 import os
 import sys
+from six.moves import input
 import time
 
 import stacktrain.core.helpers as hf
@@ -230,7 +231,7 @@ def main():
         if args.target == "basedisk":
             print("Basedisk exists: %s" % conf.get_base_disk_name())
             print("\tDestroy and recreate? [y/N] ", end='')
-            ans = raw_input().lower()
+            ans = input().lower()
             if ans == 'y':
                 logger.info("Deleting existing basedisk.")
                 start_time = time.time()