Use six.moves.input instead of raw_input (#3961)

* Use six.moves.input instead of raw_input

* Remove comment mentioning raw_input

lib/spack/llnl/util/tty/__init__.py

@@ -30,6 +30,7 @@
 import struct
 import traceback
 from six import StringIO
+from six.moves import input
 
 from llnl.util.tty.color import *
 
@@ -164,7 +165,7 @@ def get_number(prompt, **kwargs):
     number = None
     while number is None:
         msg(prompt, newline=False)
-        ans = raw_input()
+        ans = input()
         if ans == str(abort):
             return None
 
@@ -197,7 +198,7 @@ def get_yes_or_no(prompt, **kwargs):
     result = None
     while result is None:
         msg(prompt, newline=False)
-        ans = raw_input().lower()
+        ans = input().lower()
         if not ans:
             result = default_value
             if result is None: